Tropical Depression Sixteen Forecast to Hit U.S. Gulf Coast as Hurricane This Weekend

Oct 4 2017 11:00 PM EDT
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A new tropical depression formed Wednesday in the western Caribbean Sea.

This system will bring locally heavy rain to parts of Central America the next few days.

Bands of heavy rain and wind may affect Cancún and Cozumel by Friday.

It is increasingly likely the future “Nate” will make landfall along the northern Gulf Coast Sunday as either a tropical storm or hurricane.

Interests in Mexico’s Yucatan Peninsula, western Cuba and the U.S. Gulf Coast should monitor the progress of this system closely.

Tropical Depression Sixteen is heading toward the Nicaragua coast and is increasingly likely to pose a threat to parts of the U.S. Gulf Coast as a strong tropical storm or a low-end hurricane this weekend.

(MORE: Hurricane Central)

Current Storm Status

Current Storm Status

The highest cloud tops, corresponding to the most vigorous convection, are shown in the brightest red colors. Clustering, deep convection around the center is a sign of a healthy tropical cyclone.

A hurricane watch has been issued for Mexico’s Yucatan Peninsula from Punta Herrero to Cabo Catoche, meaning hurricane conditions are possible within the watch area within 48 hours.

Tropical storm warnings have also been issued for parts of the Caribbean coasts of Nicaragua and Honduras – from Sandy Bay Sirpi, Nicaragua, to Punta Castilla, Honduras – meaning tropical storm conditions are expected somewhere within the warning area, in this case within 12 to 24 hours.

Hurricane or Tropical Storm Watches/Warnings

Hurricane or Tropical Storm Watches/Warnings

A watch means hurricane or tropical storm conditions are possible within 48 hours. A warning means those conditions are expected within 36 hours.

Once the system reaches tropical storm status, it will be named Nate.

First Up: Central America/Mexico

Environmental conditions over the western Caribbean Sea and southern Gulf of Mexico are already favorable for additional strengthening.

Wind shear is currently low, and western Caribbean Sea water temperatures are currently in the mid- to upper 80s, about 2 to 5 degrees above average.

(MORE: September 2017 Was the Most Active Month on Record for Atlantic Hurricanes)

Current Sea-Surface Temperatures

Current Sea-Surface Temperatures

The system will likely track close to the northeast coasts of Honduras and Nicaragua through Thursday, then near parts of Mexico’s Yucatan Peninsula – including Cancún and Cozumel – Friday, perhaps lingering into early Saturday.

The main impacts there will include bands of locally heavy rain, elevated surf and some stronger wind gusts.

Areas of locally heavy rain from a larger-scale “Central American gyre” (more on this feature below) are likely to persist at least into part of the weekend from eastern Mexico into Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica and, perhaps, parts of Panama.

Rainfall totals may reach 30 inches in a few locations in Nicaragua and 20 inches in Costa Rica and Panama, according to the National Hurricane Center.

This torrential rain may trigger dangerous flash flooding and mudslides, particularly over the mountainous terrain of Central America.

Forecast Rainfall

Forecast Rainfall

Heavier rain may fall where rainbands stall out for a period of a few hours, particularly over mountainous terrain.

U.S. Threat This Weekend

This weekend, upper-level high pressure over the northern Gulf Coast is expected to weaken as a southward plunge in the jet stream carves into the central U.S.

Therefore, future “Nate” is expected to be pulled north into the Gulf of Mexico, steered by the combination of upper-level high pressure centered near or east of the Bahamas and what is known as a Central American gyre (again, more on this gyre is located at the bottom of this article).

Upper-Level Steering Winds for Future 'Nate'

Upper-Level Steering Winds for Future ‘Nate’

It is now likely the system will make landfall along the northern Gulf Coast, somewhere between Louisiana and Florida, Sunday. It remains too soon to tell where exactly this landfall will occur.

Most guidance also suggests this landfall will most likely be as a low-end hurricane. However, intensity forecasts are notoriously tricky this far out in time and may change.

Speaking to that point, National Hurricane Center forecaster Eric Blake noted in the 5 p.m. Wednesday advisory that rapid intensification (at least 35-mph maximum wind increase in 24 hours or less) is a possibility with this system in the northwest Caribbean Sea or Gulf of Mexico thanks to the aforementioned deep, warm water and low wind shear environment.

However, too much land interaction with Central America or the Yucatan Peninsula would likely limit the amount of intensification despite the other favorable conditions.

Here’s a general timeline of events with this system, regarding the U.S. Gulf Coast:

Saturday: Last day to prepare; some outer rainbands, swells may arrive along the eastern Gulf Coast

Sunday: Landfall, peak impact along the northern Gulf Coast somewhere from southeast Louisiana to Florida; heavy rain spreads inland into parts of the Southeast

Monday: Nate inland, but heavy rain/flood threat spreads into the Appalachians, other parts of the Carolinas, East

Projected Path

Projected Path

The red-shaded area denotes the potential path of the center of the tropical cyclone. Note that impacts (particularly heavy rain, high surf, coastal flooding) with any tropical cyclone may spread beyond its forecast path.

For now, all interests along the U.S. Gulf Coast from Louisiana to Florida should monitor the progress of this system closely. We’ll have the latest forecast updates here at weather.com and will add details as they become clearer in the coming days.

(MORE: 2017 Already a Top 10 Most Active Hurricane Season)

What Spawned This? More on Central American Gyres

This latest tropical system originated on the eastern end of a larger feature, called a Central American gyre.

This “gyre” is a large, broad area of low pressure over the Central American isthmus and western Caribbean Sea. This feature can lead to the development of a tropical cyclone in the Caribbean Sea and/or in the eastern Pacific Ocean.

These gyres most often form in the late spring and early fall, when cold fronts become uncommon in this region of the world. They’re most common in September, but can be a source of tropical storms and hurricanes into November, and as early as May.

We typically see up to two gyres like this one set up each year, and they can spawn tropical storms in both the Atlantic and eastern Pacific basins, sometimes in each basin at the same time. Not all gyres produce tropical cyclones, but they all produce heavy rainfall.

Roughly 50 percent of Central American gyres have a tropical cyclone associated with them, according to Philippe Papin, Ph.D. candidate at the University of Albany. “When a tropical cyclone does occur, it tends to form on the eastern side of the [gyre] and rotates counterclockwise around the larger circulation.”

Gyre-like tropical systems are much more common in the western Pacific closer to southeast Asia, where the monsoon plays a larger role in the weather.

A notable example of gyre-induced tropical cyclone formation occurred in 2010 when Tropical Storm Nicole formed just south of Cuba from the gyre in late September.

Nicole was a short-lived and ill-formed tropical storm that tried to cross Cuba. It brought heavy rain to the Cayman Islands, Jamaica, Cuba and portions of South Florida.

Satellite images showing the evolution of Nicole from a gyre, Sept. 26-29, 2010.  (NASA/Aqua/MODIS)

Hurricane Stan in 2005 is another good example of a hurricane’s interaction with a Central American Gyre, according to Papin.

Following Stan’s dissipation over the mountains of central Mexico, its remnant spin became part of a larger gyre that caused heavy rainfall over Central America. While Stan’s direct circulation resulted in around 80 deaths, according to the National Hurricane Center, heavy rainfall resulting from the gyre took more than 1,000 lives across Central America.

Other examples include Tropical Storm Andrea (2013), Hurricane Ida (2009 – assist from the gyre) and Hurricane Patricia (2015 – assist from the gyre, not a direct result).

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