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Hurricane Matthew Spares Florida Major Winds; Dangerous Storm Surge and Rains Arrive

By: Jeff Masters 4:16 PM GMT on October 07, 2016

Hurricane Matthew has spared Florida the worst. A mighty Category 4 storm with 140 mph winds when it devastated Grand Bahama Island on Thursday, Matthew underwent a collapse of its inner eyewall on Thursday evening, which resulted in the hurricane weakening dramatically. Now a Category 3 storm with 120 mph winds as of the 11 am EDT Friday advisory, Matthew has yet to generate sustained winds of hurricane force anywhere in Florida, though a gust of 107 mph was recorded on Cape Canaveral this morning. Matthew’s center came within 30 miles of Cape Canaveral, but the western eyewall of the storm has, for the most part, remained barely offshore today.

Figure 1. Hurricane Matthew radar at 11:33 am EDT Friday, October 7, 2016, as seen on our wundermap with the storm surge layer turned on. Storm surge levels of 1.2 - 2.4’ were along the east coast of Florida.

Intensity forecast: a slow weakening of Matthew
Satellite loops on Friday morning showed a solid but not spectacular major hurricane, with plenty of heavy thunderstorms with cold cloud tops in the eyewall. However, the eye had gotten less prominent since Thursday, and the intensity of the thunderstorms had decreased. Matthew will encounter steadily more unfavorable conditions for intensification over the next three days. Wind shear, now a moderate 15 knots, will rise to the high range, above 20 knots, by tonight. The ocean temperature will cool as Matthew progresses to the north, and dry air will be attacking from the west. The combination of cooler ocean temperatures, high wind shear and dry air should act to significantly weaken Matthew to a Category 1 hurricane by Saturday night, when it will make its closest approach to North Carolina.

Figure 2. Heavy rainfall from Matthew will be a huge concern, particularly over coastal South Carolina and southern North Carolina, as this graphic from the NWS in Wilmington, North Carolina illustrates.

Track forecast: landfall risk is greatest in South Carolina
Matthew is tracking right along the coast of Florida today, and we can expect that portions of the coast may occasionally see the west eyewall of the storm move over. This will bring hurricane-force wind gusts, but not sustained hurricane-force winds of 74+ mph. There is perhaps a 20% chance that Matthew will take a wobble to the west that would take the core of the hurricane ashore over the coast between Daytona Beach and Jacksonville, bringing sustained hurricane-force winds to the coast, though. The greater danger of hurricane-force winds at the coast is to South Carolina. The 00Z Friday runs of our four top models for forecasting hurricane tracks—the GFS, European, UKMET and HWRF—showed that Matthew will track very close to the coast of Florida and Georgia today and early Saturday morning, then potentially make landfall on the coast of South Carolina Saturday morning near 6 am EDT. The 06Z Friday runs of the GFS and HWRF model showed this, as well. The range of solutions for these various model runs was to take the storm inland by up to 30 miles or keep it offshore by about 30 miles, just south of Charleston. In their 11 am EDT Friday Wind Probability Forecast, NHC gave highest odds of hurricane-force winds in South Carolina to Charleston (45%.) The highest odds in North Carolina were at Bald Head Island (22%), and the highest odds in Georgia were at King’s Bay (37%).

While it’s going to be a close call whether or not Matthew makes landfall in South Carolina, this drama is not going to be the major factor controlling how much total storm damage occurs there. Matthew is likely to be a weakening Category 2 storm when it makes its closest approach to the South Carolina coast, and the amount of wind damage the storm can deliver to the state will be modest, even if it makes a direct hit on Charleston. The bigger threat to South Carolina is storm surge and fresh water flooding damage, which will happen to South Carolina regardless of whether or not the eye moves ashore or remains just offshore. Rainfall amounts in excess of a foot are expected along the coast of South Carolina and into southern North Carolina, in a region where soils are saturated and rivers are high due to near-record heavy rains over the past few weeks. Matthew’s heavy rains are likely to result in major damaging flooding, which will be magnified by the fact rivers won’t be able to drain into the ocean due to storm surge.

Record to near-record storm surge possible in far north Florida, Georgia, and South Carolina
Matthew’s failure to move inland and weaken over central Florida is good news for them but bad news for the coasts of north Florida, Georgia, and South Carolina. A stronger Matthew means a larger storm surge farther to the north. Matthew’s eyewall replacement cycle (ERC) was also a good news/bad news situation: while the ERC reduced the hurricane’s peak winds from Category 4 to Category 3, strong winds have now spread out over a wider area, which will increase the storm surge, due to all the extra water that will be put in motion by an expanded wind field. To illustrate, tropical storm-force winds extended 160 miles to the northeast of Matthew’s center at 11 am Thursday, but by 11 am Friday, these winds had expanded to extend outwards 185 miles from the center. At 11 am EDT Friday, the coast from just south of Cape Canaveral, FL to just south of Wilmington, NC was under a storm surge warning under a prototype NHC system expected to become operational next year. As Matthew moves northward, the northeast winds ahead of it will pile water against the coastline, leading to what could be record or near-record storm surges in some areas. The Friday morning discussion from the NWS in Charleston, South Carolina warned that:

Persistent and strong northeast winds have allowed for numerous previous tide cycles, even at low tide, to reach far above predicted levels. This pattern will continue and get even more hazardous as Matthew approaches the area from the south later today and tonight. There will be at least moderate coastal flooding with the midday high tide, but it's the high tide around 12-2 am tonight that's the most concerning when significant coastal flooding will likely occur. Tide levels are forecast to approach or even surpass those during October of 2015, meaning levels could exceed 8.0 ft MLLW at Charleston and more than 11.0 ft MLLW at ft. Pulaski. This would be the second highest crest on record for Ft. Pulaski, exceeded only by hurricane David which produced a 12.21 foot crest in 1979. It would also be in the top 5 or 10 crests on record for Charleston. These levels will be accompanied by moderate or heavy rains, creating an extremely dangerous situation for coastal areas and in downtown Charleston. Tybee Island will become cut off!

The forecasted inundation continues to be 4-8 ft for South Carolina and 7-11 ft for Georgia. Some coastal locations could experience the worst storm surge since Hurricane Hugo with devastating impacts.

Update: The 11 am Friday NHC advisory reduced the expected peak storm surge inundation for Georgia to 6 - 9 feet.

Major storm surge flooding had yet to materialize from Matthew on Friday morning at any of our tide gauges on Friday morning--though there were reports of serious storm surge flooding occurring in St. Augustine, Florida, where we do not have a tide gauge. At 11 am EDT Friday, persistent onshore winds associated with Matthew’s circulation were pushing a storm surge of 2.4 feet to the Florida/Georgia border at Fernandina Beach, 2.0 feet to Jacksonville, Florida at Mayport Bar, 1.2 feet to Savannah, Georgia near Fort Pulaski and 1.4 feet to Charleston, South Carolina, as seen on our wundermap with the “Storm Surge” layer turned on, or the NOAA Tides and Currents storm page for Matthew, or storm surge expert Dr. Hal Needham’s U-SURGE page for Matthew. Dr. Needham has some excellent information on the storm surge history of the north Florida to southern South Carolina coast in a Friday morning blog post, The "Protected Coast" is Now the Most Dangerous Place of All.

Long range forecast for Matthew: a loop-de-loop
Our top two hurricane track models—the GFS and European—continue to show high pressure building in to the north of Matthew this weekend, blocking the hurricane’s forward path. Matthew is expected to loop back towards the south and southwest, potentially reaching The Bahamas by Tuesday. Along the way, though, Matthew may draw close enough to Hurricane Nicole to force the two storms to rotate around a common center—something known as the Fujiwhara effect. This behavior can occur when two storms get within 800 miles of each other. This potential interaction with Nicole on Sunday and Monday makes the 3 - 5 day forecast for Matthew’s track of higher uncertainty than usual-though if anything, it is most likely to reinforce the expected northward track of Nicole and southward track of Matthew. One thing we are confident of: Matthew will be a much weaker storm by Tuesday when it makes its closest approach to the Bahamas. High wind shear of 30 - 50 knots is expected to affect Matthew Sunday through Tuesday, along with very dry air—humidities at mid-levels of the atmosphere are expected to drop to 20% by Monday, which is bound to cause significant weakening of the storm. If Matthew does pass through The Bahamas on Tuesday, it would likely be no stronger than a 35 mph tropical depression.

Figure 4. Track forecasts from the four European model ensemble members [gray lines] that most closely match the operational run [red line] during the first 72 hours, starting at 00Z Friday, October 7, 2016. The red line is a version of the 00Z Friday operational model track that has been adjusted and calibrated using a proprietary technique to account for systemic model errors. All of these forecasts show Matthew doing a loop over the waters east of The Bahamas, with three of them showing Matthew moving through The Bahamas. The high-probability cluster (grey lines) perform better than other ensemble members at forecast times of five days and beyond. The grey crosses along the Gulf Coast are the locations of oil wells, as this forecast tool was designed primarily for use by the oil and gas industry. Image credit: Climate Forecast Applications Network (CFAN).

We’ll be back with our next update by late this afternoon. Meteorologist Steve Gregory is making regular updates on Matthew.

Jeff Masters
Calm before Hurricane Matthew
Calm before Hurricane Matthew


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