June 16, 2024

Tropical disturbance, unusually hot ocean likely to fuel Gulf Coast flooding this week

6/16/2024 12:27:00 PM Leave a Reply

A tropical disturbance slowly moving into the western Gulf of Mexico will bring copious amounts of rain over the next couple of days, leading to a threat for flash flooding across coastal portions of Texas and Louisiana.

Forecasters expect the heaviest precipitation to fall over coastal Texas, where 5-10 inches of rain is possible through the middle of the week. Locally higher totals are possible. The region has famously poor drainage—especially the Houston metro area—so the likelihood of flash flooding during heavy rain is almost a given.

Remember, never try to drive across a flooded roadway. It's impossible to tell how deep the water is until it's too late, and the road may be washed out beneath the floodwaters. It only takes a few inches of moving water to lift up a vehicle and carry it downstream.


The slug of moisture is arriving with a tropical disturbance moseying into the western Gulf of Mexico. The National Hurricane Center gives the area a 60 percent chance of developing into a tropical depression over the next few days as it moves into the region.

Heavy rain is coming whether or not this develops into a named system. Some of the worst heavy rain events are the result of unnamed tropical disturbances—just look at what happened in Florida last week.


A tropical disturbance sent a vast amount of tropical moisture streaming over southern Florida. Persistent thunderstorms developed over the region, wringing out that moisture in the form of drenching rains that fell at several inches per hour at times.

Some areas wound up with more than two feet of rain, with the National Weather Service's latest precipitation analysis showing even more than that over the past ten days.

This latest tropical disturbance is a reminder that the Atlantic Ocean is open for business—and this season could mean business.

All major hurricane forecasts are calling for an extremely active hurricane season with predictions rivalling the busiest seasons on record. We could see more than 20 named storms this year if the forecasts pan out.


Extremely warm sea surface temperatures are driving those forecasts—and they're also likely driving the persistent heavy rain we've seen (and will soon see) across the Gulf Coast.

Warmer waters raise air temperatures over the ocean, allowing the air to hold more moisture than it would otherwise. It's likely that warmer sea surface temperatures are increasing the amount of moisture we're seeing over the region, which is enhancing rainfall totals in turn.

How unusually warm is the ocean right now?


Sea surface temperature anomalies are running 1-2°C above normal throughout almost the entire tropical Atlantic basin. 

Compare that to this time last year, where the extent and intensity of anomalies were still ugly, but a little less intense than we're dealing with this year:


It's worth noting that last year's very warm temperatures were able to fuel one of the most active hurricane seasons on record, overpowering the influence of El Niño which tends to subdue tropical activity in the Atlantic. 

This year, though, we've got even warmer waters and a La Niña in the Pacific, which is favorable to tropical development in the Atlantic. It could be a long, rainy summer. Hold on.

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March 22, 2024

Heavy snows, flooding rains likely as weekend coastal storm looms

3/22/2024 08:58:00 PM Leave a Reply

An ugly weekend is shaping up along much of the East Coast as a potent low-pressure system rolls up the Atlantic seaboard.

Our developing system will feed on plenty of moisture streaming in from the south. This ample reserve of evaporated paradise will fuel heavy rains for much of the I-95 corridor, as well as bountiful snows across interior sections of New England.

This low-pressure system was already impressive in its infancy as it got its act together across the southeastern states on Friday.


Powerful thunderstorms rocked the southern tip of Florida, prompting tornado warnings and flash flood alerts across the Florida Keys.

There was even a remarkable long-lived supercell thunderstorm that tracked along the north-central shores of Cuba on Friday afternoon, dropping very large hail west and south of Havana.


We'll see this storm intensify as it rolls up the coast into Saturday, producing very heavy rains along its track. Expect widespread downpours to envelop the I-95 corridor from Richmond to Boston through the day Saturday, lingering into Saturday night for many areas.

Most communities will see several inches of rain in a relatively short period of time. Flash flood watches are in effect from Washington, D.C., up to Boston in anticipation of flooded roads and rising waters on vulnerable creeks.


Farther north, our moisture-laden storm will run into a slug of cold air that'll allow impressive snows to plaster towns from the New York's Tug Hill Plateau all the way through northern Maine. 

The National Weather Service expects more than a foot of snow to blanket the Adirondacks, much of Vermont, northern New Hampshire, and almost all of interior Maine west of I-95.

(Forecast graphic via NWS Caribou)

Things get tricky closer to the coast, where temperatures hovering around freezing will make for mixed precipitation types throughout the storm. Snow will give way to periods of freezing rain or plain ol' rain through Saturday night, then change back over to all snow on Sunday as cold air wraps around the departing system.

Folks around Augusta and Bangor may see an extended period of freezing rain during the switch on Saturday. Areas that see more than one-quarter of an inch of ice accretion may see tree damage and power outages.

The good news, at least, is that this storm isn't going to linger. This weekend's quick-hitting thump will give way to calm conditions and warming temperatures by the beginning of next week.

[Satellite image via NOAA]

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September 30, 2023

'We had no warning'—NYC flash floods test our strained attention economy

9/30/2023 09:16:00 PM Leave a Reply

'We had no warning' is one of the most worrying and upsetting things anyone in the weather field can hear in the aftermath of an impactful storm. The latest wave of flash flooding that swamped much of New York City brought up the endless argument between 'we had no warning' and 'there was plenty of warning.'

The forecasts and warnings leading up to the storm were solid, with the risk for serious flash flooding in New York City appearing in forecasts well before the first downpours. But even so, the deluge seemed to arrive by surprise for countless folks across the city who voiced their displeasure over the apparent atmospheric broadside.

For years, folks in the weather field have personally shouldered the enormity of this problem. "It's our fault if people aren't getting the warnings," the conventional wisdom goes.

I'm not convinced anymore that it's entirely a problem on the communicators' side.

An overlooked issue seems to be that weather is taking up less space than ever in the attention economy. Warnings seem to be falling through the cracks because more folks are simply tuning them out—and I'm not sure that's something anyone can fix. 
NYC encounters another historic downpour
New York City has suffered plenty of historic rainstorms in the past couple of years, but the deluge on on Friday, September 29, will go down in history as one of the city's worst on record.

Much of the densely populated metro area saw 5-8+ inches of rain in short order between Thursday and Friday. The onslaught of water quickly overwhelmed the network of storm sewers that funnel runoff away from the concrete jungle. cascades of water pouring through the streets, into basements, and into the tunnels of the city's vaunted subway network.


It was a well-predicted disaster. Meteorologists pointed out the potential for torrential rains several days in advance, and local forecasters communicated the risk or flash flooding long before the first rain started falling.

The Weather Prediction Center issued a moderate risk for flash flooding across the NYC metro area by the middle of Thursday afternoon, and flood watches and flash flood warnings were hoisted with plenty of lead time to reach people in harm's way.


JFK Airport recorded a total of 8.58 inches of rain during the ordeal, 7.97 inches of which fell on September 29th alone, making for the airport's wettest day since records began back in 1948. 

Unfortunately, there's a vast gulf between issuing great forecasts and those excellent lead times actually reaching people in harm's way.
Warnings only matter if they're heard
A quick scroll through social media shows how much folks in the region were taken by surprise once the waters started rising. 'We had no warning' was a common complaint, as was criticism of the city's own preparation for the widespread flooding issues.

The uproar was amplified after New York's mayor bluntly criticized his own critics in a radio interview, saying "if anyone was caught off guard, they had to be living under a rock."

It's admittedly tough for meteorologists to put out warning after warning—and for officials to put emergency preparations in place—only to catch flack after the storm from folks who never heard about the threat for imminent danger.


After all, what good is a warning if the people who need it don't hear it?

Meteorologists always strive to improve forecast and warning lead times, trying their best to communicate hazards as far in advance as science and confidence will allow. This week's deluge likely would've taken folks by near-complete surprise not long ago.

Forecasters and news outlets always need to improve communication efforts. But it's a tough process. Experimenting with language as simple as the difference between "warning" vs. "emergency" is a yearslong social science project. (Take a look at NWS HazSimp if you want an inside look at how tweaking basic terms is a major effort.)

But meteorologists and emergency managers and bloggers and politicians can only do so much. The best forecasts and loudest warnings are only good if they reach the people who need them.
Our attention is stretched dangerously thin
The concept of an "attention economy" is real. We only have so much attention to give, and every aspect of our lives is competing for a piece of that finite mental real estate.

Our forms of entertainment are much different today than they were just ten years ago. Emergency alerts on television and radio reach far fewer people now that the vast majority of folks use streaming apps for shows and music.  

Apps make our phones chirp at us non-stop. It's easy to miss a flash flood warning in between breaking news alerts, advertisements, friend requests, texts, emails, and endless push alerts from games and sports apps and shopping and on and on. That doesn't even begin to cover wireless emergency alerts, which folks often disable after one too many ill-timed tests or Amber Alerts.

And then there are weather apps. We've all got apps on our phone that give us a high, a low, a chance of rain, and a cute icon with the day's weather conditions. Unless you've got a really, really good app, though, you're missing context. Words matter. Nuance is important. But they require more attention than a simple number or icon.

Most of those apps will tell you the chance of rain is 100%. For the most part, those same apps won't fill you in on the potential for excessive rainfall that could lead to widespread street flooding. We're giving up nuance in the never-ending quest to ration our well-worn attention.

So I'll give you the answer that most meteorologists, emergency managers, news organizations, and responders either can't or won't give: Each of us is ultimately responsible for our own safety. Much as folks don't want to admit it, a huge part of emergency preparedness falls on each one of us simply staying aware of what's going on every day.

The potential for flooding in and around New York City was well-advertised well in advance. Flash flood warnings went out with plenty of lead time.

People who routinely follow the weather knew that the past 48 hours would be rough across the region. 

People who don't, largely didn't.

Seeking out detailed weather information beyond a sleek icon and two numbers should be a normal part of everyone's daily routine. The weather is fine most days. Some days, though, it's not, and a few of those days will see dangerous conditions that could threaten your safety.

It can feel like a chore to have to read weather forecasts if you're not already interested in the day-to-day happenings in our skies above. But for all the humdrum updates on clear skies or gusty winds, there will be days where tornadoes are possible or a hurricane is on an unsteady course or 8 inches of rain could fall on the streets of New York City.

It's rare that a truly devastating weather event takes weather forecasters by surprise anymore.

It shouldn't take the rest of us by surprise anymore, either.

[Satellite image via NOAA]

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July 9, 2023

Widespread flash flooding possible in New England through Tuesday

7/09/2023 01:58:00 PM Leave a Reply

A pretty serious flooding situation could develop over much of New England over the next couple of days as a deep reserve of tropical moisture fuels persistent heavy rains throughout the region.

The Weather Prediction Center issued a moderate risk for excessive rainfall across most of interior New England today and tomorrow, with the best chance for flash flooding across New York's Hudson Valley and just about all of Vermont and New Hampshire.

An upper-level low swinging over the region will pull in plenty of moisture from the south. This disturbance will spark widespread showers and thunderstorms, which will easily tap into that vast reservoir of tropical moisture aloft to produce very heavy rainfall.

Source: WPC

Forecasters expect 5-7 inches of rain to fall across this area, much of which may fall in a relatively short period of time. Rainfall rates should easily exceed flash flood thresholds, pushing waterways beyond their limits and likely exceeding the capacity for storm sewers to handle the runoff.

The region's rugged terrain makes flash flooding and landslides a particularly dangerous hazard. Road washouts are likely in areas hit by flooding. Use extreme caution if you're in the area over the next couple of days. It only takes a few inches of moving water to lift a vehicle and carry it downstream.

The risk for road washouts enhances the potential that there may not even be a road anymore beneath the moving waters. It's impossible to tell how deep the water is—or if the road is even still there—before it's too late.

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September 1, 2021

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

9/01/2021 10:20:00 PM Leave a Reply

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 2, 2021

Some Parts Of The Southeastern U.S. Could See 5-7+ Inches Of Rain This Week

8/02/2021 08:22:00 PM Leave a Reply

Several rounds of heavy rain could lead to flash flooding in parts of the southeastern United States this week.

An upper-level trough parked over the Great Lakes and Ohio Valley will drive the bouts of rain moving over the southeast this week.

Tropical moisture will ride along a stalled frontal boundary like train cars on railroad tracks, leading to a couple of batches of heavy rain through the end of the week.

Some spots could pick up more than half a foot of rain. The heaviest rain is likely from the Florida Panhandle to eastern North Carolina, with Tallahassee, Savannah, Charleston, and Wilmington on track to pick up 3-5+ inches of rain in the latest 7-day precipitation forecast from the Weather Prediction Center. 

It's interesting and unsettling to watch this kind of weather event play out from a weather communications standpoint.

If a named tropical storm were on track to produce 5-7+ inches of rain in the southeast, it would be the top trend on social media and it'd garner wall-to-wall news coverage. Without the name...there's hardly anything.

It's scary to see these events potentially sneak up on people because they're not aware or not paying attention.

Make sure flash flood alerts are activated through your smartphone's wireless emergency alerts feature. Plan to avoid areas known to flood, and keep several options open to get around town if you have to go out during or after heavy rain.

Please, please remember that it's never safe to drive across a flooded roadway. It's impossible to tell how deep the water is until it's too late, and it takes only a few inches of moving water to lift up a vehicle and carry it downstream.

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May 18, 2021

More Significant Flash Flooding Is Possible Across The South Through Thursday

5/18/2021 05:08:00 PM Leave a Reply

Thunderstorms will pose a significant threat for flash flooding across parts of Texas and Louisiana over the next couple of days, with the threat for more than half a foot of rain possible in some communities this evening through Thursday. Stubborn thunderstorms already produced destructive flooding across Louisiana on Monday evening, and some of those same areas could see even more heavy rain to come.


Flash flood watches cover a significant portion of the southern United States this evening, including a huge chunk of Texas, most of Louisiana, and parts of Oklahoma, Arkansas, and Mississippi.

The greatest threat for widespread flash flooding appears to exist in Texas and Louisiana, where the Weather Prediction Center issued a moderate risk for excessive rainfall for Tuesday, Wednesday, and Thursday. The WPC mentioned on Tuesday that they might upgrade parts of Texas to a high risk for flash flooding on Wednesday—these high risks are reserved for days when forecasters are confident that excessive rainfall could lead to significant flash flooding (and it usually does).

The agency's latest rainfall forecast calls for five or more inches of rain across a huge portion of eastern Texas, with isolated pockets of extreme rainfall totals that could lead to major flooding problems in vulnerable areas. This includes the cities (and suburbs) of Houston, San Antonio, Austin, Dallas, and Corpus Christi. 


We've already seen significant flash flooding over the past 24 hours in Louisiana, where persistent thunderstorms led to flash flood emergencies around Lake Charles and Baton Rouge. Local officials had to conduct water rescues to save residents trapped by waters that rose too fast to escape. The flooding in Lake Charles is especially gut-wrenching given that the community was hit so hard by category four Hurricane Laura in August 2020 and again by Hurricane Delta two months later.

The region is at risk of excessive rainfall because of a slow-moving upper-level trough that's meandering over the southern Rockies. This is the same trough that brought a tease of rain to California over the weekend and led to so many photogenic supercells on the Plains.

Southerly winds flowing between the trough to the west and a building ridge of high pressure to the east will pump humid air northward from the Gulf of Mexico. Any thunderstorms that form in this soupy airmass will have a deep reserve of moisture to tap into, and these heavy storms can linger over the same areas for hours without much in the way of prevailing winds to steer them along. 

The northern and western Gulf Coast is exceptionally vulnerable to flash flooding during high-intensity rainfall events like this. Low, flat, and soggy terrain makes drainage a challenge even during a routine summertime thunderstorm. The combination of persistent high rainfall rates, poor drainage, and communities spreading ever farther into flood-prone areas all leads to fairly routine flash flood emergencies these days. The increasing frequency of heavy rain events (likely influenced by a changing climate) makes matters worse.

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