October 10th, 2017

Hurricane Nate

Posted at 5:04 PM ET

hurricane-nate-smHurricane Nate made landfall on October 7 near the mouth of the Mississippi river and then near Biloxi, Mississippi as a Category 1 hurricane on the Saffir-Simpson Scale. Maximum sustained winds at landfall were 85 mph, according to the National Hurricane Center (NHC). Nate is the fourth hurricane to make U.S. landfall in the past two months and the first hurricane to make landfall in Mississippi since Hurricane Katrina (2005).

The hurricane brought coastal flooding due to storm surge along with tropical-storm force wind gusts and heavy rainfall to affected areas. Downed trees and powerlines along with light property damage have been reported, along with flooding due to storm surge for affected coastal properties in Mississippi and Alabama. The severity of the hurricane was tempered by its rapid forward motion and an incomplete structure. Impacts in coastal Mississippi were further tempered by resilience measures implemented following Hurricane Katrina (2005).

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Hurricane Nate track and estimated winds; Source: NOAA/NHC

Hazard data illustrated in the CAT-i map was taken from GC AdvantagePoint®, Guy Carpenter’s web-based risk management platform. GC AdvantagePoint users can view impacted areas on any map as well as see how their portfolios were affected. Please contact your broker or cat modeling analyst for further information.

Prior to U.S. landfall, Nate passed over Central America as a tropical storm, causing very heavy rainfall with flash-flooding and mudslides, extensive damage and at least 30 fatalities, according to media reports. It will take time to fully assess the scope and severity of this event and our first thoughts and concerns are with those directly affected.

Meteorological Discussion

The origins of Hurricane Nate were from a broad area of low pressure and cyclonic circulation (called a gyre) located over Central America. An area of related thunderstorm activity was able to consolidate and develop into a tropical depression from this feature. Advisories on Tropical Depression 16, the precursor to Nate, were first initiated by the NHC on October 4, at which time tropical storm warnings were issued by the NHC for certain areas of Central America and then for certain areas of Mexico on the Yucatan Peninsula. During the morning of October 5, the feature was approaching the coast of Nicaragua with maximum sustained winds of 35 mph.

The feature was reclassified as Tropical Storm Nate at 8 a.m. EDT (12 UTC), October 5, with maximum sustained winds of 40 mph as Nate was approaching the Nicaraguan coast. At 11 a.m. EDT (15 UTC) tropical storm warnings were then issued for certain areas of Mexico in the Yucatan Peninsula while Nate crossed into Honduras. The broader circulation of Nate, together with local topography produced excessive rainfall amounts together with significant flooding, flash-flooding and mudslides over affected areas of Central America including Costa Rica, Honduras and Nicaragua.

At 11 p.m. EDT, October 5 (03 UTC October 6), hurricane, tropical storm and storm surge watches were issued for certain areas of the U.S. Northern Gulf Coast under potential threat. Tropical Storm Nate at the time carried maximum sustained winds of 40 mph. The storm then moved offshore of the Honduras coast toward the northwestern Caribbean Sea, where it began a period of rapid intensification due to warm waters and reduced wind shear, but tempered by an incomplete structure and a notable increase in forward speed. The accelerating forward speed was a result of factors including a building subtropical ridge over the West Atlantic, and another trough of low pressure crossing into the western Gulf of Mexico.

By 11 a.m. EDT (15 UTC), October 6, Nate had gained a forward speed of 21 mph, with maximum sustained winds of 50 mph. Hurricane, tropical storm and storm surge warnings were then issued for certain areas of the U.S. Northern Gulf Coast under expected threat. Meanwhile, the last of the tropical storm warnings were cancelled for affected areas of Central America. Nate then passed between the Yucatan Peninsula and western Cuba. Land interaction with the Yucatan Peninsula and western Cuba may have tempered the degree of intensification, but to a lesser degree than if the center of circulation had directly crossed the land area.

After Nate emerged into the southern Gulf of Mexico, it was upgraded to hurricane status by the NHC at 11:30 p.m. EDT, October 6 (03:30 UTC October 7), with maximum sustained winds of 75 mph and a central pressure of 988 millibars (mb). Cuba and Mexico had discontinued all tropical storm warnings as of 5 a.m. EDT (09 UTC), October 7, as Nate then moved into the central Gulf of Mexico.

By 11 a.m. EDT (15 UTC), October 7, Nate had gained maximum sustained winds of 90 mph, making Nate a strong Category 1 hurricane on the Saffir-Simpson Scale. Further intensification was limited by an incomplete structure, the 26 mph forward speed of the storm and eventually an increase in wind shear. By 5 p.m. EDT (21 UTC) Nate had attained its lowest central pressure of 981 mb on approach to the north-central Gulf Coast.

According to the NHC, Hurricane Nate made its first U.S. landfall near the mouth of the Mississippi River at around 8 p.m. EDT, October 7 (00 UTC October 8), with maximum sustained winds of 85 mph, a Category 1 hurricane on the Saffir-Simpson Scale. The minimum central pressure at the time was 982 mb. A second landfall was reported by the NHC at 1:30 a.m. EDT (0530 UTC), October 8, near Biloxi, Mississippi, with maximum sustained winds still at 85 mph, and a minimum central pressure of 984 mb. A storm surge of 6.3 feet was observed unofficially at Pascagoula, Mississippi, while Nate made landfall, with unofficial surge reports of 4.58 inches in Saint Bernard Parish, Louisiana, and 4 feet near Dauphin Island, Alabama. A wind gust of 75 mph was unofficially reported from an observing site in Calvert, Alabama, while another unofficial wind gust of 70 mph was reported at Keesler AFB in Biloxi, Mississippi. Storm force gusts were unofficially reported across the Deep South.

Following final landfall on coastal Mississippi, Nate weakened rapidly due to land interaction and wind shear while quickly moving inland. Nate was downgraded by the NHC to tropical storm status at 5 a.m. EDT (09 UTC), October 8, while the center was near the Mississippi-Alabama border. Nate was then downgraded to tropical depression status at 11 a.m. EDT (15 UTC), October 8, while the center was over northern Alabama, at which time all remaining coastal tropical watches, warnings and advisories were discontinued by the NHC.

Nate then continued to race across eastern Tennessee and Kentucky while undergoing extratropical transition (into a frontal system). Preliminary rainfall totals reported by the National Weather Service (NWS) include 6.94 inches at Dixon, Alabama; 8.32 inches at Crestview, Florida; 4.56 inches at Keesler AFB in Biloxi, Mississippi; 6.36 inches at Scaly Mountain, North Carolina and 6.12 inches near Greenville, Kentucky, with lower amounts elsewhere.

By the morning of October 9, Nate carried maximum sustained winds of 20 mph and was located over northeast Ohio, with the heaviest rain located well north and east of the center of circulation. While heavy rainfall was an ongoing hazard, rainfall accumulations were limited by the very fast forward speed of the storm. Nate still continued to pose a threat of flooding and flash-flooding due to heavy rain along with gusty winds for certain areas from the Appalachians to the eastern Great Lakes to the Northeast including areas of Southern Ontario Canada.

Hurricane Nate is the first hurricane to make landfall in Mississippi since Hurricane Katrina (2005). Nate is also the third hurricane to make landfall on the Continental United States in 2017, the first time this has occurred since the 2008 season.

Impacts

Hurricane Nate has been responsible for at least 30 fatalities in Central America, according to media reports. No fatalities have yet been reported in the United States, but at least one person was injured when a tree fell on a building in Tallapoosa, Georgia. A state of emergency has been declared in Louisiana, Mississippi, Alabama and the Florida Panhandle, and President Trump has also issued federal emergency declarations for each of these states.

Media reports indicate light structural damage due to wind for affected buildings, with damage offset in part by limited winds at landfall as well as stringency of local building codes for affected areas. Light to moderate structural damage, including foundational damage due to combined heavy rain and storm surge is possible, and flooding due to storm surge was reported for several coastal properties. Some roads and bridges suffered inundation and several affected highways were closed including US-90 in Harrison County, Mississippi.

Alabama

In Alabama, the storm flooded homes and cars on the coast and inundated at least one major road in downtown Mobile. Several homes were damaged by downed trees and a billboard was also blown down. Some flooding due to storm surge was reported for roads, houses and cars on Dauphin Island, and minor damage was reported in Orange Beach. A handful of water rescues were reported in Mobile County. As of early this morning, 50,000 households in Alabama were without power, according to media reports.

Several tornadoes were reported on the east side of the storm. One confirmed waterspout moved ashore in Gulf Shores, but no damage or injuries were reported.

Mobile Regional Airport closed on Saturday afternoon and was re-opened by noon on Sunday.  The Port of Mobile also closed Saturday, forcing an itinerary change for the Carnival Fantasy cruise ship, among other impacts. No damage to the terminal and port has been reported, but to date officials have not set a reopening date. Rough conditions continued to threaten Mobile’s navigation channel on Monday.

Mississippi

Damage has been reported for at least 25 structures in Mississippi, and power outages have affected at least 250,000 households. According to the Mississippi Emergency Management Agency, 1,100 people were in Mississippi shelters as of Sunday morning.

The storm surge coincided with high tide in Mississippi, causing substantial flooding to several coastal properties including resorts and casinos, as well as parts of US-90. Authorities cited stricter building codes and other measures taken after Katrina as factors that mitigated storm impacts.

Louisiana

Lowland areas of Louisiana were evacuated in anticipation of the storm, and media reports indicate that damage was less severe in Louisiana than in other areas. The Lake Pontchartrain Causeway Bridge was reopened by Sunday morning in both directions.

Florida

Power outages have affected several thousand people and media reports indicate that at least 3,000 households were still without power as of this morning. Pensacola International Airport closed Saturday evening but was back in service by Monday morning.

North and South Carolina

Tornado warnings were issued for the western parts of North and South Carolina. In North Carolina, the NWS confirmed one tornado southeast of Morganton and another that caused damage to a church in Caldwell County. Near Lenoir and in Burke, multiple homes were damaged and some residents were reportedly trapped in their homes. In South Carolina, a probable tornado ripped off the roof of several houses in Liberty, and a separate probable tornado downed multiple trees and power lines in Norris and near Pickens, according to media reports.

Heavy rainfall of 3 to 6 inches was expected in western North Carolina through midday Monday, with up to 10 inches in isolated locations. Power outages, some property damage and roads closed due to debris have been reported in the area.

Gulf of Mexico

Oil and gas production in the Gulf of Mexico was significantly impacted. According to the Federal Bureau of Safety and Environmental Enforcement, approximately 92 percent of current daily oil production and approximately 77 percent of the daily natural gas production was shut down as a result of Hurricane Nate. As of Sunday, 1.62 million barrels per day of oil and 2.5 billion cubic feet per day of natural gas output remained offline, almost unchanged from Saturday.

In anticipation of the storm, offshore oil and gas operators in the Gulf evacuated personnel from 302 of the 737 manned platforms and 13 of the 20 non-dynamically positioned rigs, and 16 dynamically positioned rigs were moved off location. As of Sunday, personnel on platforms and rigs were returning to work, and oil and gas operators were beginning to assess facilities to resume operations. No physical damage has yet been reported to offshore assets.

Cruise ships were also affected by the storm. At least 11 ships altered their itineraries because of Nate, including eight Carnival cruises and three Royal Caribbean ships, according to media reports.

Central America

Heavy rains, flooding, and landslides have caused extensive damage and at least 30 fatalities in Costa Rica, Nicaragua and Honduras. Media sources report blocked roads, destroyed bridges and damaged houses. In Costa Rica, some 400,000 people are without running water and thousands are now in temporary shelters.

Sources: Reuters, Associated Press, AIR Worldwide, RMS BBC, CNN, The Weather Channel, The National Hurricane Center, National Weather Service

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Guy Carpenter publishes CAT-i reports for major natural catastrophes worldwide. These reports cover catastrophes including worldwide tropical cyclones, earthquakes, major UK and European floods and any other natural event that is likely to incur a significant loss to the (re)insurance industry. Please email CAT.i@guycarp.com if you wish to be added to the free email distribution list.

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