November 25, 2021

Another Drenching For The Pacific Northwest, Heavy Snow Headed For Northeast

It's been a remarkably quiet Thanksgiving across most of the United States. There are no severe thunderstorms to worry about. No massive nor'easters threatening to disrupt every major hub on the East Coast. The tropics are blissfully quiet. The only worrisome weather this holiday weekend seems confined to the two northern corners of the country, with another atmospheric river in the Pacific Northwest and heavy snow in interior New England.

Pacific Northwest Drenching

Yet another atmospheric river has its sights set on the Pacific Northwest over the next couple of days. It's already raining over much of western Washington and southwestern British Columbia, and there's plenty more on the way over the next couple of days.

We've heard a lot about "atmospheric rivers" lately. An atmospheric river is an area of elevated moisture in the upper atmosphere that usually flows from the tropics to the mid-latitudes. These features act like reservoirs that storm systems and thunderstorms can tap into and wring out tremendous amounts of moisture.

A recent atmospheric river event brought catastrophic flooding to parts of British Columbia and Washington, the damage from which essentially cut off access to the Vancouver, B.C., metro area by land. The current bout of heavy rain and gusty winds won't be nearly as prolific as the recent storm, but lots of rain is on the way and the added stress will exacerbate the damage and effects.

The heavy rain will wash over Washington and British Columbia in several waves. The first wave is ongoing tonight through Friday. The next round of heavy precipitation will move ashore late Saturday and stick around through Monday. A third batch of heavy rain will follow soon after and arrive by the middle of the week.

The Weather Prediction Center calls for hefty rainfall totals across the region, especially at higher elevations. 5-10 inches of rain could fall along the Cascades and Coastal Range, which is likely going to compound the damage in hard-hit areas, especially in British Columbia. Lower rainfall totals are expected in the big cities.

Wintry New England

The opposite northern corner of the United States is the other area expecting the week's most active weather. A winter storm moving across Eastern Canada will bring heavy snow to parts of the interior Northeast through this weekend.

Several inches of snow are likely in higher elevations across much of New York, Vermont, New Hampshire, and Maine, with an inch or two likely at lower elevations. The heaviest totals are likely in northern Maine, where some communities could wind up with double-digit snowfall totals by Sunday. Bands of lake-effect snow will also beef up totals along the eastern shores of Lake Erie and Lake Ontario.

[Satellite Image: NOAA]

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November 10, 2021

Season's First Big Snowstorm Set To Hit Northern U.S. Plains, Canadian Prairies

It was a sunny 77°F here in beautiful central North Carolina today, and we're staring down the season's first major winter storm up north. (Sorry.) 

Some areas are on track for legitimate blizzard conditions once the snow arrives on Thursday and Friday. The heaviest accumulations will fall near and north of the border, where some areas are on track to see double-digit snowfall totals by the end of the storm on Friday. 

The impending winter storm is winding up this evening as a low-pressure system moves into the Upper Midwest. The system will strengthen in a hurry as it treks into Minnesota during the day on Thursday, producing heavy snow on the cold side of the low and heavy rain on the warm side to its south.

For areas expecting snow, conditions will deteriorate during the day on Thursday and likely peak in intensity Thursday night into Friday morning. Precipitation will taper off through the day on Friday as the system weakens and pulls out of the region.

The best chance for shovelable snow will follow close to the U.S./Canadian border, where some communities straddling the international line could see as much as a foot of snow by the end of the storm. Farther south, a few inches of snow is possible throughout much of eastern North Dakota and western Minnesota, with the chance for a dusting pushing into the Minneapolis/St. Paul area.

My map uses the National Weather Service's snowfall forecast as of Wednesday night, which is why Canada is sadly excluded from all the fun. The Weather Network calls for a widespread swath of 8-16 inches of snow across southern Manitoba and northern Ontario. (Full disclosure—I occasionally contribute to TWN.)

Gusty winds are going to be a problem, as well. High wind warnings and wind advisories are in effect for much of the northern Plains as winds could gust 60+ MPH during the height of the storm. The combination of high winds and accumulating snow could lead to a period of blizzard conditions in northeastern South Dakota overnight Thursday into Friday.

[Model Image: Tropical Tidbits]

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November 5, 2021

A Pesky Coastal Storm Will Drench Parts Of The Southeast This Weekend

A developing nor'easter will bring dreary conditions to the coastal southeast this weekend, with cool temperatures, pouring rain, and driving winds making things miserable from northern Florida to eastern North Carolina.

The storm is already in its formative stages over northeastern Florida this evening. It's not all that impressive on satellite imagery—unless a bland deck of stratus clouds is your thing, then more power to you—but it's going to slowly grow more organized over the next day or so as it meanders up the coast.

The system and its worst conditions will peak during the day on Saturday, slowly winding down on Sunday as the system pulls away from shore.

This will be a nor'easter that doesn't affect the northeast. Nor'easters get their name from the northeasterly winds that buffet the coast. There's going to be plenty of that over the next few days. Winds could gust as high as 40-50 mph in parts of South Carolina and North Carolina.

Strong and persistent onshore winds will lead to widespread coastal flooding from storm surge, especially around high tide. Coastal flood warnings are in effect from Jacksonville, Florida, to southeastern Virginia through the next couple of days.

Heavy rain is going to be a problem near the track of the storm. The bulk of the heavy rain will stay juuust offshore, but a few inches of rain are likely throughout coastal counties from northeastern Florida to eastern N.C.

These totals could inch higher if the storm tracks a little farther west than currently predicted. Any amount of heavy rain is a headache if it falls too quickly, but leaf-clogged gutters and storm sewers will increase the risk for street and parking lot flooding in some areas.

Saturday is going to be a raw and gloomy day for much of the southeast. Northeasterly winds will lead to cold air damming, a phenomenon where cold air pools up at the foot of the Appalachians because it's too dense to flow up and over the other side. Widespread high temperatures in the 50s are likely as far south as northern Florida. Conditions will warm up a bit on Sunday as the storm moves away.

[Satellite Image: NOAA]

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October 19, 2021

Multiple Rounds Of Heavy Rain Heading For The West Coast Through Early Next Week

An active pattern will send multiple waves of drenching rain into the West Coast this week, bringing measurable rainfall from the central California coast straight up through coastal British Columbia. The heaviest rain will fall at higher elevations—with heavy mountain snow likely in California—but just about everyone from Santa Barbara to Seattle has some much-needed rain on the way.

The impending bouts of heavy rain will be the result of several atmospheric rivers, or bands of enhanced upper-level moisture that flow from the tropics to the mid-latitudes. Atmospheric rivers act like reservoirs that can boost rainfall rates.

The latest 7-day precipitation forecast from the Weather Prediction Center shows 5+ inches of rain falling across a huge portion of the West Coast. As usual, higher terrain near the water will see higher totals, while cities at lower elevations or in rain shadows will see lower rainfall amounts. High elevations are going to get thumped with a decent amount of snow by this time next week.

This is going to be a long-duration event with the potential for three or four rounds of precipitation through early next week.

The first wave of precipitation is arriving in northern California this evening, and it'll sweep through the Pacific Northwest throughout the day on Wednesday. The second round, associated with a front extending off a low heading into British Columbia, will arrive overnight Thursday and taper off through Saturday. A third big wave of precipitation, which is likely going to be the most significant of the bunch, will hit on Sunday and last through early next week.

Make sure wireless emergency alerts are activated on your smart phone in case flash flood warnings or evacuation orders are issued for your location. Stay mindful of the threat for landslides and mudslides. If you come upon a flooded roadway, it's not worth trying to drive across. It's impossible to tell how deep the water is before it's too late, and it only takes a few inches of moving water to lift up a vehicle and carry it downstream.

A couple of crummy days on the West Coast are certainly more than worth it after such a hot and dry summer. 

A huge swath of the western United States remains mired in a significant drought. Last week's update of the U.S. Drought Monitor found that 87.18% of the entire state of California in an extreme or exceptional drought, the two highest categories on the scale. The impending rains and mountain snow will bring some beneficial relief to these areas. It won't erase the drought or undo the damage, but anything helps.

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October 12, 2021

A Hurricane's Remnants Could Bring Flash Flooding To Texas This Week

Tropical Storm Pamela will make landfall on Mexico's West Coast as a hurricane late Tuesday night and quickly push inland over the next few days. Mexico's rugged terrain will tear the storm to shreds in a hurry, but the system's remnant moisture will continue into the south-central United States and bring a threat for flash flooding to Texas over the next couple of days.

The National Hurricane Center expects Pamela to regain hurricane strength before making landfall near Mazatlán overnight Tuesday into Wednesday morning. The system will quickly fall apart as it grates up against the steep mountains of central Mexico. However, a deep reserve of tropical moisture will continue flowing into Texas on Wednesday and Thursday.

Pamela's remnant moisture will reach central Texas at the same time as a cold front sweeping in from the west. Add in even more moisture flowing in from the Gulf of Mexico, and additional upper-level lift from the jet stream, and it sets the stage for very heavy rainfall across the region.

The latest forecast from the Weather Prediction Center calls for widespread rainfall totals of 2-4 inches for much of central Texas on Wednesday and Thursday, with the possibility for 5+ inches of rain in some areas. This may not sound like much, but the ground here is much more impermeable than in places like Alabama or Virginia. 

The WPC issued a moderate risk for excessive rainfall (in other words, flash flooding) across the areas expecting the highest rainfall totals. A moderate risk is usually a decent signal that widespread flash flooding is likely.

As such, flash flood watches are in effect for a wide swath of Texas and a portion of southeastern Oklahoma. The watches include San Antonio, Austin, Dallas, and Fort Worth. Flash floods are dangerous no matter what, but they're especially dangerous when they occur in heavily populated areas.

Driving through floodwaters is never worth it. It's impossible to tell how deep the water is until it's too late—or if the road is even still there under the water—and it only takes a small amount of moving water to lift up a vehicle and carry it downstream.

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October 9, 2021

Tornadoes Possible Sunday As Severe Weather Threat Targets The Southern Plains

A potent risk for severe weather will cover parts of the southern Plains on Sunday as a low-pressure system develops and moves across the area. It's been a relatively quiet year across the region as far as tornadoes go, but Sunday's threat could change that in a hurry. Make sure you're prepared for severe weather and have a way to receive warnings if you're in the area this weekend.

A low-pressure system will develop over western Texas during the day on Sunday and push across Oklahoma through the evening hours. Warm, humid air will provide plenty of fuel for thunderstorms to bubble up, while ample wind shear will give those storms the kick they need to turn severe.

The Storm Prediction Center issued an enhanced risk for severe weather for a large portion of Oklahoma, including the Oklahoma City and Tulsa metro areas. Sunday's severe risk also extends outward to include Dallas-Fort Worth to the south and Joplin to the north.

Any of Sunday's severe thunderstorms could produce tornadoes, large hail, and damaging winds. The greatest threat for tornadoes and large hail will occur in and around the enhanced risk area during the afternoon hours as the storms first develop. This initial batch of discrete thunderstorms will be able to maximize their interaction with instability and wind shear.

As the evening progresses, we'll likely see thunderstorms evolve into squall lines and bow echoes. The damaging wind threat will take over as the main risk when that happens, along with a threat for spin-up tornadoes along the leading edge of any of the lines.

The threat for severe thunderstorms will continue after dark for many areas at risk on Sunday. Given that we tend to tune out after sunset, it's more important than ever to get severe weather warnings the moment they're issued. 

If you live in the region (or if you're visiting for the weekend), take a look at your phone's settings and ensure that wireless emergency alerts are activated for tornado warnings and flash flood warnings. 

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October 4, 2021

A Stormy Pattern Will Bring Heavy Rain To The Southeastern U.S. This Week

Bouts of heavy rain will envelop parts of the southeastern United States over the next couple of days as a pokey upper-level low hangs around over the region. While we shouldn't see any organized severe weather, any of the thunderstorms that bubble up in the soupy airmass could produce heavy rainfall, leading to a risk for flash flooding in some spots.

The big weather story for most of the country this week is that the weather is going to be relatively boring. A huge upper-level ridge parked over the U.S. and Canada will keep things pretty warm for the next week, with high temperatures in the 60s and 70s reaching as far north as Hudson Bay. (That's toasty for October!)

However, an upper-level low over the southeast will keep things interesting through the end of the week. This cutoff low will linger for the next couple of days, providing the lift needed to kick off several rounds of showers and thunderstorms from Alabama to Virginia.

The Weather Prediction Center's latest rainfall forecast through next Monday shows a widespread region of 2-4 inches of rain falling from the northern Gulf Coast up the Appalachian foothills into Virginia. Some areas will see higher rainfall totals, especially if any productive thunderstorms park over one area for too long.

Flash flood watches are in effect for parts of Alabama and Georgia ahead of the heavy rainfall. It's already raining pretty hard in spots. A heavy storm delayed a race at Talladega earlier this afternoon, and we had one of the year's better storms today here in central North Carolina.

The rain is a welcome sight. It was a pretty dry September for much of the southeastern and Mid-Atlantic states, with many areas coming in several inches of rain below average over the past 30 days. 

[Satellite Image: NOAA]

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September 27, 2021

Hurricane Sam Remains A Powerful Major Hurricane Over The Open Atlantic Ocean

Hurricane Sam spent more than 24 hours as a powerful category four storm this weekend as it churned out in the open Atlantic Ocean. The system was an absolute powerhouse for much of Saturday and Sunday, flirting with scale-topping category five intensity before the hurricane's structure stumbled on Sunday evening.

The latest update from the National Hurricane Center reported that Hurricane Sam's maximum sustained winds had dropped a bit to 145 mph by 11:00 p.m. on Sunday night, down from a maximum intensity of 150 mph earlier in the day. It's likely weakened some more since then given its ragged appearance on satellite imagery.

Hurricane Sam was a textbook example of rapid intensification if there ever was one. The system grew from a newly formed tropical storm to a hurricane in just about 24 hours.

The storm underwent another period of explosive intensification that began Friday evening and didn't finally level out until Saturday night when the storm reached solid category four intensity.

One of the great ironies of powerful hurricanes is that they're incredibly fragile systems. One hiccup can send them spiraling into a mess (can't we all relate these days?). That's what happened to Sam on Sunday night.

It's likely that Sam is undergoing an eyewall replacement cycle (ERC) right now, which occurs when the storm's eyewall degrades and is replaced by another, larger eye.

An ERC weakens a storm's winds and allows its minimum pressure to rise, all while redistributing its energy farther out from the center of the storm. This allows the hurricane to grow in size before potentially restrengthening once a new, stable eye emerges.

Hurricane Sam is one of the most impressive storms we've seen in the Atlantic Ocean in quite a while, and that's saying something given all the nonsense we've been through recently. It's a guilt-free gawk fest, one of the rare hurricanes in recent years we can admire without immediately cringing in fear.

Sam was a picturesque hurricane at its peak. The storm had a clear, bold eye that was surrounded by a dense core of ferocious thunderstorms fueling the system's immense power.

The near-symmetrical core of the storm vented into the upper levels of the atmosphere with a healthy outflow adorned by a beautiful plume of cirrus clouds that radiate clockwise from the eye of the storm. A hurricane's outflow exhausts air away from the eyewall so the storm is free to gather as much instability as it can from the warm ocean below.

The hurricane doesn't look that impressive anymore. Between the eyewall replacement cycle and possibly some wind shear throwing it off balance, Sam looks a little worse for wear tonight. Despite the storm's appearance, it remains a major hurricane.

Hurricane Sam is traveling around a large ridge of high pressure parked over the central Atlantic Ocean. It's crawling at just 7 mph, a relatively slow speed that's the result of weak steering currents hustling the storm along. 

Forecasters expect Sam to continue slowly lumbering along a northwesterly path that takes it safely clear of the Leeward Islands over the next couple of days.

While the storm will miss the Caribbean and likely won't have any direct impacts to the U.S. East Coast, this predicted path would bring the hurricane close to Bermuda by next weekend. We also have to watch where it goes from there for potential impacts in Atlantic Canada by the first week of October.

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September 19, 2021

Tropical Storm Rose Forms, Hurricane Season Set To Exhaust The List Of Names...Again

Tropical Storm Rose formed way out in the eastern Atlantic Ocean on Sunday evening, becoming the 2021 Atlantic hurricane season's 17th named storm. We seem to be on track to exhaust this season's official list of names for only the third time, which would rank this year among 2005 and 2020 in terms of hyperactivity. 

Peter and Rose

There's not much to say about these storms. Peter and Rose (which sounds like they could be an awful 60s folk duo) are both puttering away out in the Atlantic Ocean. Peter is a few hundred miles northeast of the Leeward Islands, while Rose is out near the Cabo Verde Islands. 

Neither of the two storms is very impressive. Peter is struggling against wind shear and Rose is on a doomed track that will terminate with its demise by the end of next week.

Both of the storms should fall apart before they reach land, and neither will come anywhere close to the United States or Puerto Rico.

We're (Probably) Going To Run Out Of Names

Barring some unprecedented and unforeseen shutdown of all tropical activity in the Atlantic Ocean for the rest of the year, it's extremely likely that we're going to run out of names again.

We only have four names left on 2021's list after Rose: Sam, Teresa, Victor, and Wanda.

One of the biggest "whoa" moments of the historic and hyperactive 2020 hurricane season is that we ran out of names by the middle of September when Tropical Storm Wilfred formed.

There are only 21 names on each season's list of hurricane names. We skip the letters Q, U, X, Y, and Z for lack of suitable replacements should one be retired.

If 22 or more storms ever developed in a single year, the plan was to fall back on the Greek alphabet to name each additional storm.

We burned through nine Greek letters in 2020, including five (!) major hurricanes and two—Hurricane Eta and Hurricane Iota—required retirement. The tracking map was an impossible mess to follow.

There was no plan to have to retire Greek-named storms. After all, up until 2020, storms at the very end of the list were usually weak afterthoughts that formed in November or December.

Add in the fact that several Greek letters sound the same (Zeta, Eta, and Theta each overlapped at one point) and it's no surprise that the fallback names weren't long for this world.

As a result, the World Meteorological Organization met earlier this year and decided to ditch the Greek alphabet and invent a supplemental list of hurricane names to fall back on if we ever had 22 or more named storms in a single year. (They created a similar list for the eastern Pacific basin.)

If (really, when) we reach Wanda, we'll roll over to the supplemental list for the remainder of the 2021 hurricane season, beginning with the name Adria and working down from there.

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September 11, 2021

Flooding Rains Likely In Texas; Watching Five Different Tropical Disturbances In The Atlantic

A tropical disturbance in the Gulf of Mexico has a high chance of developing into a tropical depression over the next couple of days as it moseys near the coasts of Mexico and Texas. 

Regardless of its development, the system will bring drenching rains to coastal Texas, with totals possibly climbing into the double digits for some by the end of the week.

We're also watching four other systems out in the Atlantic, each with varying chances for development heading into next week.

Gulf System + Texas Flooding

The National Hurricane Center (NHC) gives the Gulf disturbance a 90% chance of developing into a tropical depression by Monday, which is a decent display of confidence from the agency's expert forecasters.

The disturbance could become Tropical Storm Nicholas before it reaches land, but that's a big if, and it could have some significant impacts across the region whether or not it organizes and earns a name.

A surge of tropical moisture will sweep over the Texas coast over the next couple of days, providing a deep reserve of moisture for thunderstorms to tap into and produce torrential downpours across the region.

The Weather Prediction Center is calling for widespread rainfall totals of 4-8" across the Gulf Coast from southern Texas through central Louisiana. Higher totals are possible around Houston, Galveston, Beaumont, and Lake Charles, where someone could wind up with double-digit totals by this time next week.

Right now, it looks like the heaviest rain could fall between Sunday night to Wednesday night.

These rainfall totals are likely to change subject to the development and path of the system.  A stronger system would produce heavier rains along its path.

But either way, this has the potential to bring flooding rains to a region not particularly well-equipped to handle them. As always, the best advice is to remember that it's impossible to tell how deep the water is before it's too late. It's never worth risking your life or the lives of your rescuers to try to drive through floodwaters.

Four Other Atlantic Disturbances

Friday was the climatological peak of the hurricane season. Storms don't follow our puny calendars, of course, but this is about the time of the year when favorable atmospheric conditions coincide with sea surface temperatures warmed by the sultry heat of a long summer.

Even so, it's still jarring to see the NHC's tropical weather outlook map lit up like a Christmas tree. Aside from the impending tropical depression in the southwestern Gulf of Mexico, we have to watch four other systems out in the Atlantic.

Let's go from most interesting to least interesting...

30% Near The Bahamas

A disturbance could develop east of The Bahamas in a couple of days. If this system develops, it'll be worth watching for tropical development because of its proximity to the East Coast. An upper-level ridge is expected to develop over the region this week. Ridges tend to act like guardrails that, for lack of a better term, can trap tropical systems beneath them. 

It's nothing to worry about just yet, but file it away in the back of your mind. Spend the next few days thinking about what supplies you'd need to get through a power outage just in case something spins up and heads your way.

50% and 40% Near Africa

The two areas highlighted near the Cabo Verde Islands are typical tropical waves that roll off the western coast of Africa during the height of the summer. They're a looong way out, and we'll have plenty of time to watch what happens with these two disturbances.

20% Near Iberia

We seem to get at least one of these loners every year. A low-pressure system meandering in the northeastern Atlantic Ocean has a low chance of transitioning into a tropical or subtropical system this week. They usually don't cause too much harm aside from bringing foul weather to The Azores and the Iberian Peninsula.

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September 9, 2021

A Short History of Short-Lived Tropical Storms

Tropical Storm Mindy formed and made landfall in about four hours on Wednesday afternoon. The system joins an interesting list of storms that spun up and came ashore with little notice. Here's a very short history on these very sneaky storms.

Tropical Storm Mindy (2021)

Mindy formed from a tropical disturbance we've been watching for more than a week. The disturbance first popped up in the National Hurricane Center's tropical weather outlooks on August 30th, not long after Hurricane Ida made landfall in Louisiana.

The disturbance meandered over parts of Central America and Mexico before emerging over the Gulf of Mexico this past weekend. Forecasters upped the disturbance's odds of development to 30% on Tuesday afternoon and to 60% on Wednesday afternoon.
Source: NOAA/Gibson Ridge

The system developed a closed, well-defined circulation as it approached the Florida Panhandle on Wednesday afternoon. Forecasters declared the system Tropical Storm Mindy at 4:00 p.m., and the storm made landfall near Apalachicola just after 8:00 p.m.

Storms sometimes do that. It's the peak of hurricane season and the Gulf of Mexico is warm. It doesn't take much of a nudge to send a disturbance over the edge of formation when conditions are favorable for development.

Tropical Storm Bertha (2020)

Bertha formed at 8:00 a.m. and made landfall near Charleston, S.C., at 9:30 a.m.

Blink and you missed it. I don't even have a graphic for it. It was just...there and gone. Bloop.

Tropical Storm Imelda (2019)

Forecasters declared a disturbance in the northwestern Gulf of Mexico a tropical depression at 12:00 p.m. The system became a tropical storm at 12:45 p.m. Imelda made landfall in Freeport, Texas, at 1:30 p.m.

While this was another hello/goodbye storm, the ensuing floods were well-predicted.

The remnants of Imelda stalled over parts of Texas and Louisiana and produced a tremendous amount of rain over the following days, with widespread totals of 12-24"+ common around and east of Houston, with totals approaching four feet (!!!) near Beaumont.

Tropical Storm Emily (2017)

Emily escalated quickly on July 31, 2017, as it swirled toward Florida's west coast.
Source: NOAA/Gibson Ridge
8:00 p.m.: 20% chance of formation.
2:00 a.m.: 40% chance of formation.
6:00 a.m.: Tropical Depression Six
8:00 a.m.: Tropical Storm Emily
11:10 a.m.: Landfall near Bradenton, Florida with 45 mph winds.

Tropical Storm Bill (2015)

The disturbance that became Tropical Storm Bill in June 2015 became a soap opera because of its expected wind and rain impacts in Texas as the storm took its time developing in the Gulf of Mexico.
It was obvious that the system would rapidly intensify as it approached the Texas coast, but it would happen just hours before it made landfall near Corpus Christi. 

So we waited. And waited.

The disturbance finally developed into a tropical depression at 11:00 p.m. on June 15 and made landfall on Matagorda Island as a 60 mph tropical storm 12 hours later.

The bureaucratic headache that hampered the ability to issue forecasts for future-Bill was the reason we now get "potential tropical cyclones" every once and a while.

Forecasters at the National Hurricane Center came up with the PTC designation after Bill so the agency could issue advisories, watches, and warnings for a disturbance if it's going to develop and hit quickly hit land soon after. Before then, we just had to wait and wait, which wasted critical time needed to get the word out to people in harm's way.

Hurricane Humberto (2007)

Source: NHC
One of the most memorable quicker-spinner-uppers was Hurricane Humberto in 2007. The system went from a tropical depression to a category one hurricane in about 24 hours, making landfall near Beaumont, Texas, with 85 mph winds.

The storm intensified into a hurricane 15 miles off the coast.

15 miles.

Humberto's sudden jump in intensity wasn't well predicted, and folks in the path of the storm had very little time to prepared for a full-fledged hurricane—which is less of a statement about the NHC's abilities back in 2007 than it is about a tropical system's ability to take off when it thrives over the Gulf of Mexico.

[Satellite Image: NOAA]

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September 6, 2021

Large Hurricane Larry Scrapes Bermuda This Week, Dangerous Surf/Rip Currents For U.S.

Larry is a looker. This major hurricane in the central Atlantic Ocean will scrape by Bermuda later this week—possibly bringing squally weather to the island—before approaching Newfoundland next weekend. While the storm won't affect the U.S., dangerous surf and rip currents are likely as Larry's vigorous waves reach the East Coast.

The sculpted cyclone is the third major hurricane of the 2021 Atlantic hurricane season. The National Hurricane Center's Monday morning advisory found the hurricane's maximum sustained winds holding steady around 120 mph.

A ridge of high pressure over the western Atlantic will steer Larry around its outer periphery, bringing the hurricane east of Bermuda on Thursday before allowing it to recurve and head in Newfoundland's general direction next weekend.

Larry is the first hurricane we've had this year that's a stunning, largely guilt-free gawk-fest on satellite imagery.

The hurricane almost resembles a western Pacific typhoon. Hurricane Larry has a huge eye—70 miles wide!—and a near-symmetrical core. These are called annular hurricanes, and I like to refer to them as "all eyewall" because there's not much to the storm but its eye and thick inner core. 

Forecasters expect Larry's portly stature to aid the hurricane in maintaining intensity over the next couple of days. After that, the system will begin to struggle as it enters a more unfavorable environment and picks up speed as it rounds the ridge.

The storm will lose its tropical characteristics at the end of the week and transition into an extratropical cyclone, or the "everyday" type of low-pressure system that's driven by upper-level winds and has fronts at the surface.

Even so, the storm will still have hurricane-strength winds when it passes Newfoundland's Avalon Peninsula on Friday or Saturday. Larry is already a large storm, and systems tend to grow larger as they transition from tropical to extratropical, so there's a decent chance it brings some foul weather to the region if it stays on its predicted track.

The Avalon is home to about half of Newfoundland's population (roughly a quarter of a million people), so the wind and rain could be disruptive even if the center of the storm passes far offshore.


While Hurricane Larry won't come close to hitting the United States, the storm's rough surf will pose a hazard to beaches from Florida to Maine. Life-threatening rip currents are possible this week as Larry's waves reach the U.S.

Rip currents are currents that pull away from the shore. They form as a result of waves hitting the beach head-on, forcing the water to drain straight away from the coast in swift, narrow channels. Rip currents don't pull you under the water—they pull you out and away from land.

A rip current often looks like a calm spot amid a torrent of waves hitting the beach, which makes these hazardous areas alluring to visitors. If you see a curiously calm patch of water between waves, or sea foam swiftly pulling away between waves, don't go in the water, and dissuade others from going in the water as well.

The best way to avoid rip currents is to avoid going in the water when rip currents are a danger. But if you ever find yourself in a rip current, don't panic. Swim parallel to the shore until the current stops pulling you out to sea, then swim back to safety. If you can't swim, or if you don't have the energy to swim, calmly signal for help and tread water until help arrives.

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September 1, 2021

Hurricane Ida's Remnants Unleash Tornadoes, Flash Flood Emergencies In Northeast

Predictions of widespread flash flooding and an enhanced risk for tornadoes came to pass on Wednesday as the remnants of Hurricane Ida passed through the Mid-Atlantic and Northeast. Flash flood emergencies were issued across the region, including the entire New York City metro area. The system also spawned multiple strong tornadoes in Maryland and New Jersey.

This was a well-predicted event. Forecasters sounded the alarm a few days ago that this system would produce widespread and intense flash flooding in parts of the northeast, and the Storm Prediction Center had a risk for tornadoes highlighted across the affected regions for the past couple of days.

Widespread Flash Flooding

The WPC's excessive rainfall outlook for Wednesday, issued Tuesday afternoon. || SOURCE: WPC

Tropical moisture associated with the remnants of Ida flowed north on Tuesday and overran a stationary front parked over the region. This initial batch of precipitation produced drenching rains over parts of Pennsylvania, New Jersey, New York, and Connecticut, overnight Tuesday into Wednesday.

Ida's remnants then caught up with this boundary as the erstwhile tropical cyclone transitioned into a non-tropical low-pressure system.

The lift from the low and its associated fronts provided a new focal point for additional heavy showers and thunderstorms to develop on Wednesday afternoon. The intense rains continued through early Thursday morning.

These thunderstorms trained over the same areas for hours at a time, tapping into the deep reserve of tropical moisture to produce incredible, rarely seen rainfall rates for this part of the country. Central Park recorded 3.15 inches of rain in one hour between 8:51 PM and 9:51 PM.

Portions of Pennsylvania, New Jersey, and the New York City area witnessed double-digit rainfall totals by midnight on Thursday.

The torrential rains led to widespread flash flood warnings for almost the entire region, including the New York City metro area.
Many of the flash flood warnings were flash flood emergencies, enhanced wording (similar to a tornado emergency) that forecasters can use to describe widespread, life-threatening flash flooding.

This was the first time New York City had ever been included in a flash flood emergency, highlighting the high-end, historic potential of this flash flood event.

It's likely sunrise on Thursday will reveal significant damage from the flash floods across a large swath of the region.

Multiple Strong Tornadoes

The flash floods completely eclipsed the Oklahoma-style tornadoes we saw from some of the storms earlier on Wednesday afternoon.

The remnants of hurricanes are infamous for producing tornadoes as they push inland, especially systems that parallel the Appalachians after hitting the northern Gulf Coast.

Strong wind shear that's favorable for the development of tornadoes is common in the "right-front quadrant" of the storm. This is the eastern side of the storm for most systems that hit the United States.
A model-simulated sounding of the atmosphere near Wilmington, Delaware, on Wednesday afternoon. The clockwise line on the top-right graph shows strong vertical wind shear in the atmosphere, favorable for supercells that could produce tornadoes. || SOURCE: Tropical Tidbits

Winds in this part of the storm veer clockwise between the lower and mid-levels of the atmosphere, providing the strong wind shear necessary for a thunderstorm to begin rotating. As a result, we often see small supercells form in the outer bands of tropical cyclones.

The remnants of tropical cyclones (such as Ida on Wednesday) often act like a low-pressure system we'd see in the middle of the spring. Warm, humid air on the eastern side of the system provides the instability needed for thunderstorms to bubble up and thrive. These storms then tap into that rotation and go on to produce tornadoes.

We saw that situation play out as Ida passed through the region. Multiple tornadoes touched down in Virginia, Maryland, and New Jersey on Tuesday and Wednesday. 

Some of the tornadoes were downright scary, looking more like something we'd see in Oklahoma or Alabama than the Mid-Atlantic.

Annapolis, Maryland:
Mullica Hill, New Jersey:
Burlington, New Jersey:

It'll be a day or two before the National Weather Service is able to get out there and survey the damage, but it wouldn't surprise me if one or two of the tornadoes today was "significant," with a rating of EF-2 or higher.

Ida's remnants now join a long list of strong hurricanes that spawned tornado outbreaks in the days after they made landfall in the southeast.

The most infamous tropical-induced tornado outbreak in recent memory was Hurricane Ivan in 2004, which spawned more than 100 tornadoes as the system and its remnants traversed the southeast and Mid-Atlantic. One of Ivan's tornadoes produced F3 damage in Fauquier County, Virginia, just southwest of Washington, D.C.

Hurricanes Isaias, Florence, and Frances also spawned significant and memorable tornado outbreaks as they moved over the eastern states.

[Satellite Image: NOAA]

Note: I updated this post multiple times on Wednesday night to update the rainfall map and add new information.

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August 31, 2021

Tornado Threat Increases For I-95 Corridor Between D.C. And Philly On Wednesday

An enhanced risk for severe weather will exist around the Washington, Baltimore, and Philadelphia areas on Wednesday as the remnants of Hurricane Ida move through the region. There's enough wind shear that the strongest thunderstorms that form in the region could produce tornadoes.

Forecasters at the Storm Prediction Center issued an enhanced risk for severe weather—a three on the five-category scale measuring the threat for severe thunderstorms—for the I-95 corridor stretching from northern Virginia to southern New Jersey, including parts of southeastern Pennsylvania, eastern Maryland, and Delaware.

Tornadoes will be the predominant risk. Severe thunderstorms in the risk areas could also produce damaging wind gusts.

The threat will be greatest during the afternoon and evening hours on Wednesday.

While the enhanced risk area will see the best environment for tornadoes, a risk for tornadoes on Wednesday will extend as far to the south as the Charleston, S.C., area, and as far to the north as Nantucket.

Tropical Depression Ida (and soon to be "Remnants of Ida") spent Tuesday swirling over the Tennessee Valley. The system will continue heading toward the northeast over the next couple of days.

The system is undergoing extratropical transition, which means it's losing its tropical characteristics and transitioning into an everyday type of low-pressure system that's powered by upper-level winds and has surface fronts.

There's still plenty of wind shear on the eastern side of the system, which is common for landfalling tropical cyclones. This wind shear allows thunderstorms to develop rotation that can produce tornadoes.

The remnants of hurricanes that hit the Gulf Coast are infamous for the tornado potential these systems can bring to the Mid-Atlantic. If tomorrow's forecast pans out, Ida's remnants will be no exception.
SOURCE: Tropical Tidbits

The graph above reveals why there's an enhanced risk for tornadoes around the Mid-Atlantic on Wednesday.

This is a model simulation of the data we get from weather balloons, looking at temperature, moisture, and winds through a vertical slice of the atmosphere. This particular graphic is for the area around Wilmington, Delaware on Wednesday evening.

If you look at the hodograph on the top-right side of the image, you'll see a long line that hooks clockwise as it spirals out on the graph.

That tells us that winds are picking up speed and veering clockwise with height—the type of shear that makes supercell thunderstorms possible.

Make sure you have a way to receive severe weather warnings the moment they're issued. Check your cell phone's emergency alerts feature and make sure they're activated for tornadoes. Tropical-influenced tornadoes can happen quickly, and they can grow quite strong.

A threat for tornadoes isn't the only concern we'll have to deal with on Wednesday. The system's ample tropical moisture will produce widespread heavy rainfall from the Appalachians to coastal New England over the next couple of days.

Rainfall totals of 3-5" will be common, with locally higher amounts where training thunderstorms develop. This heavy rainfall will lead to a potential for flash flooding across a large stretch of the region.

The Weather Prediction Center issued a high risk for excessive rainfall (read: flash flooding) on Wednesday across portions of Pennsylvania, New Jersey, New York, and Connecticut. A high risk for excessive rainfall from the WPC is relatively rare, and it's indicative of high confidence in the potential for widespread flash flooding. 

Stay alert for flash flood warnings in addition to tornado warnings. Never try to drive across a flooded roadway. Many people die every year when they drive into a flood and drown. It's impossible to tell how deep the water is before it's too late.

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Ida's Remnants Are A Flash Flood Threat In The Mid-Atlantic And Northeast This Week

The remnants of once-powerful Hurricane Ida will bring a threat for flash flooding and tornadoes to much of the eastern U.S. over the next couple of days.

While the storm's winds are a mere shadow of their 150 MPH fury when the storm made landfall in Louisiana on Sunday, the system is still a major rainmaker and will lead to a threat for tornadoes through midweek.

Ida's remnants will pass over the Tennessee Valley Tuesday and Wednesday, reaching the Mid-Atlantic and Northeast by the end of the week.

A trough moving over the Great Lakes will catch up with Ida's remnants by the middle of the week. This trough will help the system redevelop into an extratropical cyclone, or your typical, everyday type of low-pressure system.

The combination of Ida's tropical moisture and all the extra lift from the trough and developing surface low is a recipe for very heavy rainfall. It's the atmospheric version of wringing out a soaked washcloth.

Source: WPC

Right now, the Weather Prediction Center has a moderate risk for excessive rainfall (read: flash flood potential) across a wide swath of the Mid-Atlantic and parts of the southern Northeast. 

The agency's latest rainfall forecast shows widespread totals of 3-5 inches falling along the path of ex-Ida. Locally higher totals are possible, especially where training thunderstorms produce high rainfall rates.

Stay alert for flash flooding during and after heavy rainfall. If any of your daily routes are prone to flooding, map out an alternate route ahead of time so you can avoid danger.

Many people die every year when they drive into a flood and drown. It's impossible to tell how deep the water is until it's too late, and sometimes there's not even a road under the water anymore. 

Flooding won't be ex-Ida's only hazard. There's still enough wind shear on the eastern side of the system to allow thunderstorms to begin rotating.

We'll see a tornado risk across parts of the southeast and Mid-Atlantic over the next couple of days. This risk is greatest in Alabama, Georgia, and the Florida Panhandle on Tuesday, but tornadoes are possible as far north as the Delmarva Peninsula through Wednesday.

Tropical tornadoes happen quickly, sometimes with reduced tornado warning lead time. Make sure your cell phone's wireless emergency alerts are activated so you can receive a tornado warning the moment one is issued.

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