Friday, 7 October 2016

Hurricane Matthew update - 10/06/2016


Matthew’s Nightmarish Storm Surge Takes Aim at 430-Mile Stretch of U.S. Coast

6 October, 2016

All throughout yesterday and today the story has been the same — dangerous hurricane Matthew is strengthening in a record-hot atmosphere and ocean environment as it continues to take a course that will result in severe flooding impacts for a massive swath of the southeastern U.S. seaboard.

An Extraordinarily Powerful Category 4 Hurricane

As of 5 PM EST today, the center of Hurricane Matthew was located about 25 miles to the south of Freeport Island, Bahamas. The storm was tracking off to the north-northwest, making steady progress toward Florida and a large section of the U.S. coastline. Since yesterday, maximum sustained winds have increased from around 120 mph to a present peak wind speed of around 140 mph. More importantly, the storm’s minimum central pressure is falling. As of the 5 PM advisory,the storm’s lowest pressure reading stood at 936 millibars — about 2 mb stronger than Hurricane Sandy’s peak intensity.

(A very robust Hurricane Matthew is starting to look more and more like a CAT 5 than a CAT 4 in the most recent satellite shots. That’s bad news for the southeastern U.S. coastline as this powerful storm is approaching at an oblique angle — one that, if the storm continues along its forecast track, will push a large surge of water topped with powerful breaking waves into numerous coastal communities. Image source: The National Hurricane Center.)

The National Hurricane Center notes that Matthew may have just gone through an eye-wall replacement cycle, which would result in a brief drop in maximum sustained winds. But pressures continued to drop as the storm got better organized, and now, the satellite picture shows the fearful symmetry of an extremely dangerous storm. As Matthew continues to get more organized, peak wind speeds could continue to rise, hitting 145 mph or higher before ramping wind shear and a long encounter with the U.S. mainland begins to check Matthew’s considerable strength.
Possible Flooding Rains Threaten Lake Okeechobee Dikes

As Matthew approached the coastline this afternoon, large bands of rain began to cover much of Florida even as onshore winds stiffened. Lake Okeechobee — which is now going through a series of dike upgrades to protect communities east of the lake from storm events like Matthew — is starting to see the effects of these heavy rain bands. With 4 to 8 inches or more of rainfall possible over the Lake Okeechobee region from Matthew (and up to 12 inches or more for parts of coastal Florida), pressure to a dike system needing refurbishment is likely to present serious challenges.
(Matthew’s considerable rain bands are already blanketing Florida and 4 to 12 inches are possible for parts of the state. Image source: The National Weather Service.)

The Major Hazard Comes From a Potentially Massive Storm Surge
Farther north and east, the main story is that Matthew is pushing a Sandy-like storm surge toward a 430-mile section of the U.S. coastline. 
According to the National Hurricane Center, a region stretching from Sebastian Inlet in Florida north to Edisto Beach in southeastern South Carolina could experience storm surges in the range of 7 to 11 feet. A 700-mile arc from Deerfield Beach, Florida to the Santee River in South Carolina could see surges above 4 feet.

Such a powerful storm surge over so large an area would swamp numerous coastal communities already facing the difficulties of human-forced sea level rise, like increasing cases of nuisance flooding at times of monthly and seasonal high tides. As with Sandy, Matthew’s storm surge will rush in upon this higher launching pad resulting from thermal expansion of the world’s waters, glacial melt, and ocean current shifts related to climate change.
(Considerable worst-case storm surge risks are now posed by Matthew to coastal communities like St. Augustine. As Matthew strengthened Thursday, these severe flooding potentials continued to worsen. Compare with earlier flood map here. Image source: The National Hurricane Center.)

As a result of Matthew’s continued strengthening over near record-hot waters and a moisture-laden atmosphere, prospects for coastal communities along the storm’s path don’t look very good. A 7- to-11 foot surge is enough to swamp many communities. As we can see in the image above, worst-case potential flooding (1 in 10 probability to exceed) for St. Augustine now puts that city under 3 to 10 feet of water — dramatically worse than last night’s initial storm-surge model estimates of a possible 1-to-9 foot inundation for the city.
As Matthew’s expected track runs parallel to the coastline, city after city, from Cape Canaveral to Jacksonville to Savannah to Charleston, faces the potential for similarly extreme coastal flooding as Matthew continues to rush shoreward.
Note: This is an increasingly dangerous developing weather situation. Coastal interests from the Bahamas through Florida, Georgia and the Carolinas should stay abreast of forecasts provided by the National Hurricane Center, stay tuned to local weather statements, and remain to respond to possible evacuation/emergency storm shelter information.
Hat tip to JPL

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