May 24, 2018

Flooding Rains, Gusty Winds Likely as Tropical Disturbance Approaches the Gulf of Mexico


This weekend marks the unofficial start of the summer season, so of course it's going to be absolutely miserable at some of the country's most popular vacation spots. The National Hurricane Center has given a tropical disturbance in the western Caribbean a 90% chance of developing into a tropical cyclone in the Gulf over the next couple of days. The summery weather pattern we've seen over the past two weeks will continue right into next week, and that means more tropical downpours for a region already drenched from recent heavy rains.

We're going to see heavy rain from this pattern regardless of this disturbance's development into a named system. If it feels like you've read this same post twice, it's because we went through this very ordeal just last week. The tropical disturbance in the Gulf of Mexico last week had a much lower chance of developing than the one we're watching this weekend, however, and it looks like the next five days could bring significant rainfall to parts of the southeast.

Tropical Threat


The tropical disturbance off the coast of Belize—officially called Invest 90L for now—briefly started to look more impressive on satellite imagery on Thursday. A large burst of convection developed over the tropical wave early Thursday morning and the convection sustained itself for most of the day before waning with the loss of daytime heating.

Thursday's 8:00 PM EDT outlook from the National Hurricane Center gives the system a 70% chance of developing into an organized system by Saturday evening and a 90% chance of developing within the next five days.

There's a decent chance that the NHC could start issuing advisories on this disturbance tomorrow if a surface low is able to develop near or beneath that burst of convection off the Yucatan Peninsula. If and when the system develops into an organized system, it's not out of the question for it to reach at least tropical storm strength once it makes it to the Gulf of Mexico this weekend.

The system will be named Alberto if it manages to reach tropical (or subtropical) storm strength. What will possible Alberto (possAlberto?) look like when it reaches the Gulf? Rain. Rain rain rain. Lots of rain. Tons of rain. Enough rain to cause flooding whether or not the storm gets a shiny new name or not.

It's Gonna Rain


It's been raining for a while and it's gonna rain even more. The latest rainfall forecast from the Weather Prediction Center for the next seven days—extending through May 31—calls for up to 7" of rain along the northern Gulf Coast and a widespread area of 3-4" of rain from New Orleans to Wilmington and everywhere in between. Rainfall totals will be higher in spots if persistent heavy rain and thunderstorms are able to train over the same areas for an extended period of time. And trust me, that probably will happen somewhere. It almost always does in a situation like this.

The stagnant weather pattern has already brought lots of rain to the southeast and Mid-Atlantic. Take a look at these totals over the past 14 days:


If you can overlook the horrendous color table I created for observed rainfall in my mapping software (it looks like a box of crayons effervesced!), the overall point is that there's been a ton of rain over the past two weeks and you can easily see the areas that have seen persistent thunderstorm activity. Many areas from Florida to Pennsylvania saw more than five inches of rain between May 10 and May 24, and parts of the Mid-Atlantic and southern Florida saw totals approaching (and in some spots exceeding) double digits.

Flooding is a serious concern as the disturbance moves closer to the United States, especially in areas that have seen many inches of rain. The ground is saturated and waterways are full. It won't take much of a downpour to cause issues in areas where natural and man-made water systems are taxed to begin with. Keep an eye on severe weather alerts over the next week and take a look at your smartphone to see if your wireless emergency alerts are activated.

The Wind and Waves May Be Problematic

Make sure you're ready for power outages. Trees and power lines usually don't handle gusty winds well when the ground is saturated. Lingering sogginess and upcoming rain will enhance the potential for downed trees and power lines in gusty winds. The risk for wind-driven power outages will increase if the system approaches the coast as an organized storm.

Rip currents will be a growing threat as the winds pick up ahead of the disturbance. Rip currents are fast currents of water that pull water away from the beach. Rip currents occur when waves crash directly on the beach rather than at an angle—you can sometimes spot these currents by looking for calm spots mixed in with the waves.

Don't go in the water if you're at the beach for the holiday weekend and there are red flag warnings in effect. Rip currents don't suck you under like they show in the movies. People drown in rip currents because they can't swim, panic, or get tired and can't tread water anymore. If you're ever caught in a rip current, either tread water and calmly signal for help or swim parallel to the shore until the pull stops, and then swim back to the beach.

It's also worth keeping in mind the risk for tornadoes. Tornadoes are common in the bands of tropical systems that come ashore. These tornadoes are small but they're especially dangerous because they can happen very quickly with a reduced (or even no) tornado warning lead time.

May Storms


I sure feel like I jinxed it by talking about how we might just make it through May without any named storms for the first time in a few years. Here's what I wrote last week:

It looks like we might make it to the end of May without a named system for the first time since 2014. It's not too unusual to see a named system develop before the official start of the Atlantic Hurricane Season on June 1. It happens once every couple of years. In fact, the past three years have all seen storms develop early.
My bad!

But really, if and when this thing gets a name, you're going to see sites and news networks make a huge deal about how A STORM FORMED BEFORE THE START OF HURRICANE SEASON! Here's the deal. Storms form before June 1 every couple of years. It happened to happen in 2014, 2015, and 2016. And we'll make it four years in a row if this thing develops.

It's not that unusual to see a sorry excuse for a tropical storm develop in May. They usually form in the western Atlantic or the Gulf of Mexico. What would be unusual, though, would be for this storm to gain any significant strength beyond sustained winds of maybe 50 MPH, but we'll cross that bridge if we ever get there. 

While there is evidence that the date of a season's first named storm has grown earlier over time, the streak of seeing named storms in April or May will be noteworthy if that trend keeps up for another couple of years. For now, it's probably safe to consider it a novelty statistic.

[Images: Dennis Mersereau]


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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I ran Gawker's The Vane for two years and I've contributed to Mental Floss, Forbes, Popular Science, and the Washington Post's Capital Weather Gang. I also teamed up with Outdoor Life to write a book called The Extreme Weather Survival Manual, which came out in October 2015.

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