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Tropical Depression Sixteen Forecast to Hit U.S. Gulf Coast as Hurricane This Weekend; Hurricane Watch Issued For Cancún
Tropical Depression Sixteen will track over Nicaragua and Honduras today, then target Cancún Friday night, and will then 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)
The center of the tropical depression is about to move onshore in northeast Nicaragua, moving northwest at 5 to 10 mph.
Infrared satellite imagery indicates the thunderstorms nearest to the center of T.D. Sixteen are still mainly over the southwest Caribbean Sea, however, a broad gyre of low pressure called a Central American gyre (more on that feature below) has spawned numerous clusters of thunderstorms in Central America.
Current Storm Status
A hurricane watch has been issued for Mexico's Yucatan Peninsula from Punta Herrero to Rio Lagartos – including Cancún and Cozumel – 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, in this case over the next 12 to 24 hours.
Hurricane or Tropical Storm Watches/Warnings
Once the system reaches tropical storm status, it will be named Nate.
First Up: Central America/Mexico
The tropical depression will track through northeast Nicaragua and northeast Honduras through Thursday night, bringing clusters of heavy rain, gusty winds, and some elevated surf.
After the center moves back over water Friday, environmental conditions are favorable for some additional strengthening.
Western Caribbean Sea water temperatures are currently in the mid- to upper 80s, about 2 to 5 degrees above average, and wind shear may lessen a bit.
Current Sea-Surface Temperatures
The main impacts there will include bands of locally heavy rain, which will pick up during the day Friday, elevated surf and tropical storm or hurricane-force winds.
Areas of locally heavy rain from a larger-scale Central American gyre (again, 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, 20 inches in Costa Rica and Panama, amd 12 inches in the eastern Yucatan Peninsula, according to the National Hurricane Center.
This torrential rain may trigger dangerous flash flooding and mudslides, particularly over the mountainous terrain of Central America.
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 off the southeast U.S. coast 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'
Future "Nate" 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. The uncertainty in Nate's forecast track is higher than normal.
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.
Land interaction with Central America and/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 parts of the Gulf Coast
- Sunday: Landfall, peak impact along the northern Gulf Coast somewhere from Louisiana to the Florida panhandle; 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 East
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.
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.
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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