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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