Keeping An Eye On Tropical Storm Nate

October 04 10:06 2017 Print This Article

Tropical Storm Nate is moving over Nicaragua and Honduras, and will threaten parts of the U.S. Gulf Coast as a strong tropical storm or hurricane this weekend, after passing near the resorts of Cancún and Cozumel.

The newly-formed tropical storm is currently located near the border of Nicaragua and Honduras, just inland of the Caribbean Sea, and is moving northwest at 5 to 10 mph.

According to the National Hurricane Center, Nate was upgraded from a tropical depression Thursday morning based on radar from San Andrés, and island east of Nicaragua, indicating a partial eyewall and a surface pressure measurement over Nicaragua found to be lower than previous advisories.

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 and tropical storm warning has been issued for Mexico’s Yucatan Peninsula from Punta Herrero to Rio Lagartos – including Cancún and Cozumel – meaning hurricane conditions are possible and tropical storm conditions are expected.

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 either expected or already occurring.

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.

First Up: Central America/Mexico

Nate will track through northeast Nicaragua and northeast Honduras through Thursday night, bringing clusters of heavy rain, gusty winds, and some elevated surf.

Once 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

Current Sea-Surface Temperatures

Nate will make its closest approach to Mexico’s Yucatan Peninsula – including Cancún and Cozumel – Friday night, as either a tropical storm or low-end hurricane.

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 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 will weaken as a southward plunge in the jet stream carves into the central U.S.

Therefore, Nate will pull 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'

Upper-Level Steering Winds for Future ‘Nate’

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 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 Nate 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.

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).

Source: Weather.com