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Hurricane Matthew Steadily Intensifying, Likely to be a Category 4 Storm for Florida

By: Jeff Masters 1:25 PM GMT on October 06, 2016

Powerful Category 3 Hurricane Matthew has steadily intensified over the warm waters of The Bahamas, and is poised to become a Category 4 hurricane this afternoon. An Air Force hurricane hunter aircraft penetrated Matthew’s eye at 8:17 am EDT, and found that the central pressure had fallen to 937 mb (preliminary data, not official yet.) The surface winds measured by their SFMR instrument were unchanged from what the aircraft measured in their earlier pass through the eye at 6:08 am, but the pressure fell 7 mb between those fixes—a significant drop. Matthew’s pressure was 961 mb at 11 pm EDT Wednesday, and the 24 mb pressure fall in nine hours that has occurred since then will likely lead to a further increase in Matthew’s winds, by about 10 - 15 mph, by this afternoon. This would make Matthew a 135 - 140 mph Category 4 storm as it bears down on Florida.

There is hope, though, that the current intensification cycle may be leveling off. Satellite loops at 8 am EDT Thursday 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 the early morning hours. There was no obvious cooling of the tops of the eyewall thunderstorm clouds going on, or large-scale expansion of the hurricane’s size. The 8:17 am EDT eye report from the Hurricane Hunters noted that the eyewall was open on its west side, which may halt intensification.

Figure 1. Hurricane Matthew as seen from 248-nm range Miami radar (with clutter turned off) at 8:31 am EDT Thursday, October 6, 2016. Matthew's eye was just east of Andros Island in the Bahamas, and the northern eyewall was beginning to affect Nassau, on New Providence Island.

The Bahamas getting pounded
At 2:19 am EDT Thursday, winds at a personal weather station (PWS) on Staniel Cay, Exumas, located in the strong right eyewall of Matthew, about 30 miles east-northeast of hurricane’s center, peaked at 92 mph, gusting to 101 mph. The pressure bottomed out at 984 mb at that time, and 12.95” of rain fell in the 7-hour period midnight to 7 am EDT.

WU member ExumaMET reported this from the island of Exuma, which Matthew sideswiped on Wednesday evening: Morning all. It was an intense night here. I recorded Sustained winds over 100 and gusts way into category 4 strength with one gust hitting 153mph before something took out my instrument. We're still in tropical storm force and it should be interesting to see what the island looks like as the sun comes up.

The dangerous right front quadrant with Matthew’s highest winds began pounding the most populous island in The Bahamas, New Providence, on Thursday morning around 8 am EDT. Winds at 9 am EDT at the Nassau airport were 58 mph, gusting to 85 mph, and the pressure was falling rapidly. Extreme winds are the main danger on New Providence, though a storm surge of up to ten feet is possible. Fortunately, the capital of Nassau is on the more protected north side of the island, which is less vulnerable to storm surge. High tide is at 11:46 am EDT, and the highest storm surge will likely arrive shortly before then. Tidal range between low tide and high tide is about two feet, so the timing of the high tide relative to a possible ten-foot storm surge can contribute up to a 20% increase in the observed storm tide (the height of the water above ground.)

The weaker left-side eyewall of Matthew will be punishing Andros Island late Thursday morning and into Thursday afternoon. Late Thursday afternoon, it will be Grand Bahama Island’s turn to receive a beating.

Figure 2. Enhanced infrared image of Matthew as of 8:37 am EDT Thursday, October 6, 2016.

Intensity forecast: a major hurricane for The Bahamas and Florida, but not a Cat 5
Matthew has favorable conditions for intensification: light to moderate wind shear of 5 - 15 knots, very warm ocean waters of 29.5 - 30°C (85 - 86°F) and 70 - 75% relative humidity at mid-levels of the atmosphere (as analyzed by the SHIPS model.) Matthew may get an extra bump in intensity when it crosses over the axis of the warm Gulf Stream Current Thursday evening, but the total ocean heat content will decline as the hurricane draws very near to the coast of Florida early Friday morning. Interaction with land will occur then, limiting the potential for intensification. Strong upper-level winds out of the southwest will begin bringing moderate wind shear of 10 - 20 knots on Friday, and there is plenty of dry air to the hurricane’s west that these winds will be able to drive into the hurricane’s core. By Saturday, when Matthew is near the coast of South Carolina, wind shear will rise to the high range, 20 - 25 knots, and the combination of high wind shear and dry air to the storm’s west should act to significantly weaken Matthew from Saturday through Monday as it parallels the coasts of South Carolina and North Carolina. We can expect Matthew to weaken to a Category 1 hurricane or tropical storm by Monday of next week.

The bottom line: Matthew is likely to be a major Category 4 hurricane by this afternoon, and will likely be at Category 3 or 4 strength when it affects the east coast of Florida on Friday. Matthew is not likely to become a Category 5 storm.

Florida under siege
The 00Z Thursday runs of our two top models for forecasting hurricane tracks—the GFS and European—showed that Matthew will make landfall on the coast of Central Florida early Friday morning. The 06Z Thursday run of the GFS model showed this, as well. In their 5 am EDT Thursday Wind Probability Forecast, NHC gave highest odds of hurricane-force winds in Florida to Ft. Pierce (67%), West Palm Beach (62%), and Cocoa Beach (56%).

How strong Matthew is when it affects Georgia and South Carolina is difficult to predict, as it depends strongly on how much time the hurricane spends over land in Florida. The most likely strength for Matthew at the time of its closest approach to Georgia and South Carolina is as a Category 2 storm, but a Category 1 or 3 storm is also a possibility.

We'll have much more on the threat Florida, Georgia, and South Carolina face in our next post.

Long-range track forecast for Matthew: less danger to North Carolina, no danger to New England
Thursday’s latest 00Z run of the European model and 06Z run of the GFS model predicted that Matthew would turn to the northeast and then east on Saturday, keeping the storm several hundred miles south of the coast of North Carolina. In this scenario, the coasts of Georgia and southern South Carolina would be at risk of hurricane force winds, but the coast farther north—including North Carolina and New England—would not be. In their 5 am EDT Wednesday Wind Probability Forecast, NHC was giving the coast from Jacksonville, Florida to Charleston, South Carolina 11 - 17% chances of receiving hurricane force winds. Probabilities for the coast of North Carolina were less than 10%. There is still a great danger of flooding rains in southern North Carolina, though, even if the storm passes more than 100 miles to the south. Rivers are high and the soils are saturated from heavy rains during the past two weeks, and the expected 6+ inches of rain Matthew will dump may cause widespread damaging flooding.

Figure 3. Screen shot of NHC’s interactive Storm Surge Probability product from 5 am EDT Thursday, October 6, 2016, showing the probability of inundation in excess of 5’ above ground level from Matthew. The northern Florida coast to the coast of South Carolina is expected to have a greater than 50% chance of getting inundation in excess of five feet. The highest probabilities are along the Georgia coast, where hurricane impacts are fairly infrequent. The graphic is based upon an ensemble of Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model runs created using the current National Hurricane Center (NHC) official hurricane advisory. Storm surge probabilities depend on the historical accuracy of NHC's forecasts of hurricane track, and wind speed, and an estimate of storm size.

Long range forecast for Matthew: thrown for a loop
Our top models—the GFS, European, and UKMET—continue to show Matthew missing getting picked up by the trough to its north this weekend and looping back towards The Bahamas by Tuesday next week. However, Matthew will experience high wind shear of 30 - 50 knots Sunday through Tuesday, which would make Matthew a weak tropical storm by Tuesday.

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 Thursday, October 6, 2016. The red line is a version of the 00Z Thursday operational model track that has been adjusted and calibrated using a proprietary technique to account for systemic model errors. Only one of these forecasts shows Matthew entirely missing a landfall along the Southeast U.S. coast, and all of them show Matthew failing to recurve out to sea to the northeast. 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).

Meteorologist Steve Gregory is making regular updates on Matthew.
Rapid-scan 7-minute time resolution loop of Matthew from NASA/MSFC

We’ll have several more posts today.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.