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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