Dr. Jeff Masters ·

Above: GOES-16 view of Hurricane Nate, at 12:22 pm EDT Saturday, October 7, 2017. At the time, Nate was a top-end Category 1 storm with 90 mph winds. Image credit: NOAA/RAMMB. GOES-16 imagery is considered preliminary and non-operational.

Hurricane Nate is steadily strengthening as it hurtles north-northwest at 26 mph across the Gulf of Mexico, and is likely to be a Category 2 storm at landfall Saturday night between Southeast Louisiana and the Florida Panhandle.

Nate threaded the needle through the narrow Yucatan Channel between Mexico and Cuba overnight, but the hurricane’s strongest winds and heaviest rains missed the northeast tip of the Yucatan Peninsula, which was located on the left (weak) side of the storm. The top winds on Friday in Cozumel, Mexico and Cancun, Mexico did not exceed 20 mph in their regular hourly observations, and the two airports recorded just 1.30” and 0.75” of rain, respectively.

Deadly torrential rains from Nate have affected large parts of Central America. As of Saturday morning, Nate had led to a total of 25 deaths in Central America; hardest hit were Nicaragua with 12 deaths, and Costa Rica with 9. Satellite rainfall estimates show that Nate has dumped 8+” of rain on the Pacific side of Costa Rica, Nicaragua, and Panama, and also along the northern coast of Honduras and the eastern coast of the Yucatan Peninsula, in both Mexico and Belize.

#Nate loop from @NOAA_HurrHunter aircraft's lower fuselage radar from 3:23am to 7:08am CDT Saturday. 4am CDT NHC track. (Credit: NOAA-AOC) pic.twitter.com/652TsGcbE5 — Tropical Atlantic (@TropicalATL) October 7, 2017

As of noon EDT, Nate was already bringing storm surge levels of more than 1.5’ to nearly the entire U.S. Gulf Coast. A storm surge of 2.0’ was observed at the New Canal Station in New Orleans, LA; 1.92’ in Mobile, AL; and 1.85’ in Pensacola, FL. You can track the storm surge using our wundermap with the “Storm Surge” layer turned on, or with the excellent new interactive tool from SURGEDAT.

Satellite imagery early Saturday afternoon showed that Nate had become much more symmetric, though its shape had gotten distorted by the fast forward speed of the hurricane. An eye was not yet visible. Microwave satellite imagery and data from an Air Force and a NOAA hurricane hunter aircraft showed that Nate had not yet established a completely closed eyewall, and the hurricane would likely have to do that if rapid intensification into a Category 3 storm were to occur before landfall. New Orleans radar showed that the outer spiral bands of Nate were already affecting the coast.

Figure 1. Height above ground of the storm surge inundation that has a 1 in 10 (10%) chance of being exceeded from Hurricane Nate, based on the 11 am EDT Saturday NHC advisory. The barrier islands off the Mississippi coast have the highest chances of extreme inundation, in addition to many bays along the Mississippi coast.

Forecast for Nate through landfall

Nate will continue moving briskly near 25 mph during the day, and will make landfall Saturday night between New Orleans, LA, and Pensacola, FL. Nate is projected to angle toward the north-northeast around this time, and the exact location of this turn will largely determine the landfall location. If the turn is delayed a bit, landfall could be in far southeast Louisiana, whereas a faster turn will bring the center closer to the coast of Alabama or the far western Florida Panhandle. Nate’s forward motion may slow a bit as the hurricane embarks on its rightward turn, but it is still expected to be moving at a clip of at least 18 mph. This will keep the window of peak coastal impacts relatively brief, mainly from late Saturday night into Sunday morning.

Winds

The swath of sustained hurricane-force winds at landfall is not expected to be broad—perhaps 30 miles wide, and mainly to the east of Nate’s center. Tropical-storm-strength winds could affect a much broader region, up to 150 miles wide, again focused to the east of Nate’s center. As we saw with Hurricane Irma in Florida, sustained winds below hurricane strength can still be enough to bring down trees and power lines in wet soil and produce widespread power outages.

Since Nate will make landfall as a fairly fast-moving system (around 15 – 20 mph), there will be a stronger-than-usual asymmetry to its wind field, with the bulk of the strong winds to the right (east) of Nate’s center. NOAA’s Atlantic Oceanographic & Meteorological Laboratory explains: “In general, the strongest winds in a hurricane are found on the right side of the storm because the motion of the hurricane also contributes to its swirling winds. A hurricane with 90 mph [145 km/hr] winds while stationary would have winds up to 100 mph [160 km/hr] on the right side and only 80 mph [130 km/hr] on the left side if it began moving (any direction) at 10 mph [16 km/hr]. Note that forecasting center advisories already take this asymmetry into account and, in this case, would state that the highest winds were 100 mph [160 km/hr].”

We cannot stress enough the danger of LIFE-THREATENING storm surge especially in Mobile Bay Region. Don't focus on storm category! #nate 1/2 — NWS Mobile (@NWSMobile) October 7, 2017

Storm Surge

A storm surge warning is up for the Gulf Coast from Morgan City, LA, to the Okaloosa/Walton county line in Florida, as well as along the northern and western shores of Lake Pontchartrain. A storm surge watch is in effect eastward from the warning area to Indian Pass, FL. Nate is capable of producing enough surge to cause significant coastal flooding and potential damage. The highest surge from Nate will arrive quickly on Saturday night and will most likely peak before dawn Sunday, so coastal residents need to take the surge threat seriously and make final preparations as soon as possible on Saturday.

Peak surge levels expected by NHC were raised on Saturday morning in line with Nate’s strengthening trend. As of 11 am EDT Saturday, the following inundations above ground level are possible with Nate, assuming the storm were to arrive during high tide:



Mouth of the Mississippi River to the Mississippi/Alabama border...7 to 11 ft

Mississippi/Alabama border to the Alabama/Florida border, including Mobile Bay...6 to 9 ft

Morgan City, Louisiana to the mouth of the Mississippi River...4 to 6 ft

Alabama/Florida border to the Okaloosa/Walton County Line...4 to 6 ft

Okaloosa/Walton County Line to Indian Pass, Florida...2 to 4 ft

Indian Pass to Crystal River, Florida...1 to 3 ft

Because the daily high tide across this region occurs during the pre-dawn hours, it is quite possible that Nate will reach the coast near high tide. Tidal range between low and high tide is 1 - 1.3’ along the central Gulf Coast, so the timing of Nate’s storm surge with respect to the high tide can cause an additional foot or so of flooding. High tide in Mobile, Alabama is at 1:46 am local time Sunday, and it will be one of the highest high tides of the year, due to the full moon. Low tide is at 10:12 am Saturday. At Shell Beach, LA, on the east side of New Orleans, high tide is at 4:29 am local time Sunday, and low tide is at 12:14 pm Saturday.

The surge forecasts for the Mississippi and Alabama coasts are particularly concerning. Few if any mandatory evacuations had been issued as of early Saturday morning, yet based on current forecasts, it is possible that Nate will deliver one of the higher surges in recent decades (outside of Hurricane Katrina) to parts of the surge-prone coasts of Mississippi and Alabama. At 11 am CDT Saturday, near low tide, the surge was already close to 1.8’ at Dauphin Island, AL.

Below are some of the highest storm surges on record for Mississippi and Alabama:

Mississippi:

Bay St. Louis:

• 25.0', Hurricane Katrina, 2005

• 21.7', Hurricane Camille, 1969

• 15.2', September 1947 Hurricane

Pass Christian:

• 27.8', Hurricane Katrina, 2005

• 22.6', Hurricane Camille, 1969

• 13.4', September 1947 Hurricane

Long Beach:

• 25.7', Hurricane Katrina, 2005

• 21.6', Hurricane Camille, 1969

• 14.0', September 1947 Hurricane

Gulfport:

• 24.5', Hurricane Katrina, 2005

• 21.0', Hurricane Camille, 1969

• 14.0', September 1947 Hurricane

Biloxi:

• 22.0', Hurricane Katrina, 2005

• 19.5', Hurricane Camille, 1969

• 11.1', September 1947 Hurricane

Pascagoula:

• 18.0', Hurricane Katrina, 2005

• 11.8', Hurricane Camille, 1969

• 9.0', September 1947 Hurricane



Alabama:

Mobile:

• 11.6', July 5, 1916 Hurricane

• 11.45', Hurricane Katrina, 2005

Dauphin Island:

• 9.2', Hurricane Camille, 1969

• 7.7', July 5, 1916 Hurricane

Gulf Shores:

• 11.8', September 1906 hurricane

• 9.1', Hurricane Camille, 1969

Rains

Nate’s rapid motion will limit the total amount of rainfall at any one spot, and the overall accumulations should be less than those observed during slower-moving tropical cyclones. However, Nate is embedded in a very moist atmosphere, and torrential rain could still fall in short periods. The heaviest rains are likely to be just east of the New Orleans metropolitan area, which will reduce the odds of issues with the city’s troubled storm drainage network. Localized rainfall totals of 6 - 9” are expected close to Nate’s center, from the MS/AL coast into central Alabama, and intense rainbands will stream onshore well east of Nate's center across the Florida Panhandle.

A large area of 3 - 8” rains, perhaps including Atlanta and Nashville, may develop as Nate accelerates into the southern Appalachians on Sunday. Moisture from Nate will also flow into a belt of 2 – 5” rains further north, associated with a frontal zone that will push from the Great Lakes into the Northeast. Rains of 2 - 5" will then stream across the northern Appalachians and into southern New England on Monday, as Nate races northeast along the frontal zone as a fast-weakening tropical cyclone. Much of the Northeast has been abnormally dry in recent weeks, so the Nate-related rains will be largely beneficial.

Figure 2. 3-day precipitation totals from 8 am EDT Saturday, October 7, 2017, through 8 am EDT Tuesday, October 10. Image credit: NOAA/NWS/WPC.

Nate makes a hyperactive 2017 hurricane season even more notable

Nate is the ninth hurricane of this hyperactive 2017 Atlantic hurricane season, giving it the most hurricanes since 2012. This makes 2017 tied for the 15th most hurricanes on record, according to Dr. Phil Klotzbach (Colorado State University). Nate is also the ninth consecutive named storm this year to reach hurricane strength (preceded by Franklin, Gert, Harvey, Irma, Jose, Katia, Lee, and Maria.) The last time nine or more consecutive named storms became hurricanes was in 1893, when ten did so.

If Nate makes landfall as a hurricane in the U.S., it will mark the first time since 2008 that three hurricanes have hit the U.S. mainland. In 2008, Hurricane Dolly made landfall in far southern Texas on South Padre Island on July 23 as a Category 1 hurricane, killing 3 and causing $1.5 billion in damage. On September 1, Hurricane Gustav made landfall near Cocodrie, Louisiana as a Category 2 hurricane, killing 53 and causing $7 billion in damage. On September 13, Hurricane Ike hit the upper Texas coast as a strong Category 2 hurricane, killing 112 people and causing $35 billion in damage. That year also had 3 tropical storms strike the U.S. (Edouard, Fay, and Hanna), and was the last year to see six named storms hit the U.S.

Nate will bring the total number of 2017 continental U.S. landfalls by named storms to five, in addition to the landfalls by Tropical Storm Cindy, Tropical Storm Emily, Hurricane Harvey, and Hurricane Irma. If we include Maria's landfall in Puerto Rico, the U.S. will have had six landfalls in 2017. According to Dr. Klotzbach, average continental U.S. landfalling statistics since 1900 are 3.5 named storms, 1.8 hurricanes and 0.7 major hurricanes. The highest number of tropical storms and hurricanes to hit the continental U.S. in one year was 9 in 1916; 2004 had 8, and there were 7 in 2005.

A hurricane makes landfall in the United States during October about every two years, according to Dr. Klotzbach. Florida has been the most frequent target, with 28 October landfalls since 1878. In that same period, a total of 13 hurricanes have made landfall from Texas to Alabama during the month of October.

Bob Henson co-wrote this post.