Hurricane Nate strengthening as it moves rapidly through the central Gulf of Mexico

October 07, 2017

THE WEATHER CHANNEL–Hurricane Nate is racing north-northwestward in the central Gulf of Mexico with landfall expected on the northern Gulf Coast Saturday night and Sunday, where hurricane warnings have been posted. Nate quickly intensified on Friday and is expected to continue to strengthen on Saturday. A period of rapid intensification is also possible. 

Happening Now

The latest data from NOAA and the Air Force Reserve Hurricane Hunter aircraft suggest that maximum sustained winds are at 85 mph, which makes Nate a Category 1 hurricane. 

Nate's center is currently about 245 miles south-southeast of the mouth of the Mississippi River, moving rapidly north-northwest at about 22 mph. 

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.

Conditions are improving across western Cuba and Mexico's Yucatan Peninsula and all watches and warnings here have been discontinued. Rain showers are occasionally passing through offshore Florida waters and the Florida Keys. 

Tropical storm force winds currently reach up to 125 miles mainly to the east of the center, while hurricane-force winds extend outward up to 35 miles from the center.

Current Winds

Watches and Warnings

A hurricane warning, meaning in this case hurricane conditions are expected in the area by Saturday night, is now in effect from Grand Isle, Louisiana, to the Alabama/Florida border including New Orleans and Lake Pontchartrain.

A storm surge warning has been posted from Morgan City, Louisiana, to the Okaloosa/Walton County line in Florida, including the northern and western shores of Lake Pontchartrain. This means a life-threatening inundation is likely in these areas with the landfall of Nate, in this case, Saturday night into early Sunday.

A hurricane watch, meaning hurricane conditions are possible, is in effect for much of the rest of southeast Louisiana and the Florida Panhandle from the Alabama/Florida border to the Okaloosa/Walton County line.

Current Tropical Storm Watches and Warnings

Tropical storm warnings are in effect for a similar swath of southern Louisiana currently in a hurricane watch as far west as Morgan City.

Tropical storm watches extend west of the warnings to Intracoastal City, Louisiana, and as far east as Indian Pass, Florida. Tropical storm conditions could penetrate as far inland as central Alabama and northern Georgia. 

A storm surge watch extends east of the Alabama/Florida border to Indian Pass, Florida, meaning inundating, life-threatening storm surge is possible in that area.

U.S. Forecast Timeline

Nate's center will make one or more landfalls along the northern Gulf Coast, between southeast Louisiana and the far western Florida panhandle, Saturday night into early Sunday, most likely as a Category 1 hurricane.

Due to the complex geography in the northern Gulf Coast, a landfall point remains difficult to pinpoint, but the overall track will bring Nate through the northern Gulf Coast and into the Southeast this weekend. 

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.

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

  • Saturday: Last hours to prepare; swells arrive along the northern Gulf Coast with some potential coastal flooding; outer rainbands arrive at the coast and spread inland; Tropical storm force winds arrive mid-late afternoon along the coast.
  • Saturday night: Damaging, hurricane-force winds possible in hurricane warning and possibly in watch areas; landfall expected overnight with storm surge flooding in surge flood warning and possibly watch areas; bands of heavy rain; worst of the impacts likely to the north and east of the center track.
  • Sunday morning: Again, landfall could occur in pre-dawn hours with storm surge flooding, hurricane or tropical storm-force winds near and east of the center; areas of heavy rain spread into other parts of the Southeast, southern Appalachians.
  • Sunday afternoon/night: Nate weakens over the Tennessee Valley with some lingering gusty winds but heavy, potentially flooding rain continues in the Appalachians, Tennessee Valley.
  • Monday: Lingering heavy rain, flash flooding possible in the Appalachians and parts of the Northeast.

To emphasize, preparations should be completed as soon as possible in the hurricane and storm surge warning areas, as conditions (outer rainbands, some at least minor coastal flooding) will go downhill already later Saturday morning.

U.S. Impacts

Storm Surge

Coastal flooding will already build ahead of Nate's arrival Saturday. 

The peak storm surge will occur with the closest approach of the center of Nate Saturday night or early Sunday morning.

Here are the potential peak water levels above ground you may see from storm surge, according to the National Hurricane Center. This should be thought of as the worst-case flooding expected with Nate, if the storm surge arrives at high tide.

Peak Storm Surge Forecast  The forecasts above from the National Hurricane Center are potential peak water levels above ground due to storm surge if it occurs at high tide.

Unfortunately, there is high tide during the overnight hours Saturday night as Nate's center draws near. Here are the times of high tide, in local time, for several locations that are expected to see storm surge flooding from Nate:

  • Grand Isle, Louisiana: Saturday 11:31 p.m.
  • Waveland, Mississippi: Sunday 1:20 a.m.
  • Dauphin Island, Alabama: Saturday 11:50 p.m.
  • Pensacola, Florida: Sunday 12:19 a.m.

Battering waves will also ride atop the storm surge, capable of additional damage to docks and buildings.

Current Wave Heights

Winds

Nate's wind field is not expected to be particularly large. Therefore, the greatest chance of hurricane-force winds capable of structural damage, significant tree damage, and multi-day power outages are likely to be near and east its immediate center or eyewall close to the Gulf Coast around landfall.

Due to the lopsided nature of Nate, the impacts of wind are expected to be considerably lower on the west side of wherever Nate makes landfall. 

Power Outage Potential

However, Nate's relatively fast forward speed, may push tropical storm-force winds over a larger area inland, possibly well into parts of Alabama, Mississippi, the Florida panhandle and western Georgia.

These winds are capable of at least some power outages, some downed trees, and perhaps some light structural damage.

Tropical Storm-Force Wind Probabilities  This indicates the chance of winds from 39 to 73 mph from Nate, according to the National Hurricane Center. Higher gusts can also occur even in a tropical storm.

Rainfall Flooding

A swath of 3 to 6 inches of rain, with locally up to 10 inches possible, is expected not just near the landfall area along the Gulf Coast this weekend, but also well inland through Monday into the Tennessee Valley. 2 to 4 inches of rain are expected as far inland as the mid-Atlantic.

This may trigger serious inland flash flooding Sunday into Monday in the Appalachians, as happens often with inland tropical cyclones. 

Other parts of the Ohio Valley and Northeast may also see some heavy rain, depending on the path of Nate's inland remnant.

Forecast Rainfall

Tornadoes

Isolated waterspouts and tornadoes will be possible to the east of and to the north of where Nate makes landfall, with the most likely tornado locations being from southeastern Louisiana eastward to the central Florida panhandle and inland to southern Alabama and southern Georiga. Tornadoes could begin as early as Saturday afternoon on the coast. 

Mexico's Yucatan Peninsula, Central America and western Cuba Forecast

Effects from Nate are beginning to wane across Mexico and Central America. 

Bands of locally heavy rain will become more sporadic Saturday morning in the Yucatan Peninsula and extreme western Cuba.

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 in parts of Central America and far southeast Mexico.

Here are the latest rainfall forecasts from the National Hurricane Center:

  • Eastern Yucatan Peninsula and western Cuba: 2 to 4 inches, with isolated totals as high as 6 inches
  • Eastern Belize and the Cayman Islands: 1 to 3 inches

Recap

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

Enough spin and thunderstorm activity was collected east of Nicaragua on Oct. 4 that the National Hurricane Center upgraded Invest 90L to a tropical depression. Heavy rain partially from the gyre and from newly upgraded Tropical Depression 16 spread across Central America. 

According to the National Hurricane Center, Nate was upgraded from a tropical depression on the morning of Oct. 5 based on radar from San Andrés, an island east of Nicaragua, indicating a partial eyewall and a surface pressure measurement over Nicaragua found to be lower than previous advisories. Nate moved ashore over northeastern Nicaragua and eastern Honduras later that day. 

On Oct. 6, Nate accelerated through the northwestern Caribbean and through the Yucatan Channel while organizing and intensifying. A wind gust of 52 mph was reported in Isabel Rubio in western Cuba as Nate shot the goal posts between the Yucatan and Cuba. Hurricane hunters reported a building eyewall in Nate's eastern semicircle. 

What Spawned This? More on Central American Gyres

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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