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Hurricane Matthew Now a Category 4 After Topping Out at Category 5 Strength

By: Jeff Masters 3:47 PM GMT on October 01, 2016

Hurricane Matthew weakened slightly on Saturday morning to a still-ferocious Category 4 storm after topping out Friday night as the Atlantic’s first Category 5 storm in nine years. Matthew put on a spectacular and wholly unexpected display of rapid intensification on Friday, strengthening from a tropical storm to a Category 5 hurricane in a remarkably short period of time—just 36 hours. It’s a good thing this unexpected rapid intensification burst did not occur as the hurricane was approaching landfall in a heavily populated area, with a population unprepared for a catastrophic hurricane strike. There have been other storms that have intensified even more rapidly from tropical storm strength to Category 5 than Matthew, though. For comparison, Hurricane Wilma of 2005 and Hurricane Patricia of 2015 accomplished the feat in 24 hours; Hurricane Felix of 2007 did it in 30 hours; Hurricane Rita of 2005 and Hurricane Andrew of 1992 did it in 36 hours; and the Great Labor Day Hurricane of 1935 did so in 42 hours.

Figure 1. Latest satellite image of Matthew.

What made Matthew’s rapid intensification so surprising was that it occurred despite the presence of strong upper-level winds out of the southwest that created high wind shear of 20 knots. The NHC official forecast and the intensity models failed to predict Matthew’s rapid intensification—though the SHIPS model did give a 12% chance that we would see intensification into a Category 5 hurricane. We don’t have much data over ocean areas to be able to diagnose the detailed flow pattern around the core of a hurricane, and it is likely the shear was actually much lower near Matthew’s center, which allowed the storm to organize more quickly than our models anticipated. The rapid intensification process was also aided by the fact Matthew was moving into a moister atmosphere—the upper-level winds hitting Matthew from the southwest were advecting in air that had high humidity, which did not disrupt the storm like low humidity air would have done.

Another surprise regarding Matthew’s rapid intensification was that the central pressure that supported the Category 5 winds of the storm was relatively high—941 mb. Category 5 storms usually have pressures quite a bit lower. According to meteorologist Sam Lillo, Matthew had the third highest pressure observed in an Atlantic category 5 hurricane. For comparison, Hurricane Andrew had a 933 mb central pressure when it was a Category 5, and Hurricane Felix had a 935 mb central pressure when it achieved Category 5 status. Matthew’s strongest winds have been focused over a relatively narrow region near the core of the storm, which has allowed it to have extreme winds without an extremely low pressure.

Figure 2. Radar view of Matthew’s eye as seen from the Air Force Hurricane Hunters on their Friday night flight that found Category 5 winds. Image credit: Pilot Maj Roundtree, Air Force hurricane hunters.

Current observations of Matthew
An Air Force hurricane hunter aircraft made two passes through the eye of Matthew on Saturday morning, and found that Matthew’s central pressure had risen to 947 mb during their second pass at 8:48 am EDT. Flight-level winds at 10,000 feet hit 135 mph and surface winds measured by their stepped frequency microwave radiometer (SFMR) were as high as 124 mph, which would make Matthew a borderline Category 3/Category 4 storm. Infrared satellite loops on Saturday morning showed that Matthew had weakened some, with the eye less distinct and the cloud tops of the eyewall thunderstorms warmer. At upper levels, high cirrus clouds streaming to the north of Matthew showed the continued presence of a powerful outflow channel, which was helping ventilate the storm and allowing it to fight off the high wind shear of 20 - 30 knots affecting it. Aiding development today were warm ocean waters of 28.5°C (83°F) and 70 - 75% relative humidity at mid-levels of the atmosphere, as analyzed by the SHIPS model. Heavy rains from Matthew were affecting the coast of South America near the Colombia/Venezuela border, as seen on Venezuela radar.

Two-day intensity forecast for Matthew
Matthew is about to turn the corner around the Azores-Bermuda High, and will head north-northwest on Sunday towards Jamaica and southwestern Haiti. The latest SHIPS model forecast predicts that wind shear will steadily drop during the next two days, reaching the low range, less than 10 knots, by Sunday morning. At the same time, ocean temperatures will warm to 29° C (84°F) and the heat content of the ocean will increase, which ordinarily would argue for re-intensification of Matthew. However, this morning’s hurricane hunter flight found that the eye of Matthew had shrunk to eight miles in diameter, and the aircraft showed evidence of a secondary maximum in winds outside of the eyewall. This may be an indication that Matthew is about to undergo an eyewall replacement cycle (ERC), where the inner eyewall collapses and is replaced by a larger-diameter eye, with a new eyewall formed from an outer spiral band. This process usually causes a weakening to the storm’s top winds for a day or so. It is possible that we will see little net change in Matthew’s strength before the storm makes its closest pass to Jamaica and southwestern Haiti on Monday--perhaps a decrease in peak winds today into Sunday, with some rebound possible by Monday if an eyewall replacement cycle is completed in time. The down side of an ERC is that is spreads out the storm’s hurricane-force winds over a wider area, resulting in severe impacts over a wider area.

Our top three intensity models—the HWRF, LGEM, and SHIPS models—were predicting on Saturday morning that Matthew would have top sustained winds of 120 - 130 mph on Monday. The SHIPS model gave Matthew a 0% of rapid intensification of 30 mph or more by Sunday morning. In their 11 am EDT Saturday Wind Probability Forecast, NHC gave highest odds of hurricane-force winds to Guantanamo Bay, Cuba (29%) and Kingston, Jamaica (25%.)

Two-day track forecast for Matthew
Differences continue in the two-day model track forecasts for Matthew, though the differences between our two best models—the GFS and European model—have shrunk since Friday’s runs. This may be because of dropsonde data taken by the NOAA jet on Friday evening, which was ingested into the 00Z Saturday runs of the models. A large upper-level low pressure system over east-central U.S. will begin pulling Matthew sharply to the north-northwest by Sunday, but the exact timing of the turn is in doubt. An later turn is being predicted by the 06Z Saturday run of the GFS model, with the storm passing between Jamaica and southwestern Haiti on Monday afternoon, and hitting eastern Cuba early Tuesday morning. The 00Z Saturday European model run has Matthew heading northwards a little sooner, with a landfall in southwest Haiti on Monday afternoon, and then in northwest Haiti early Tuesday morning.

Longer-range intensity forecast for Matthew
Matthew’s anticipated landfall over Jamaica/Cuba/Haiti on Monday will weaken the storm, due to the high mountains it will interact with. This process may completely disrupt the inner core of Matthew, reducing the storm to Category 1 or 2 strength for several days, as it traverses The Bahamas. The storm may be able to re-intensify to major hurricane status in 2 - 3 days, though, over the exceptionally warm waters surrounding The Bahamas. The LGEM and HWRF models predict a 25 - 30 mph increase in Matthew’s winds between Tuesday and Thursday. However, our ability to make intensity forecasts this far in advance is limited.

Figure 3. The 70 forecasts from the 00Z Saturday European (ECMWF) model ensemble (top) and GFS model ensemble (bottom) continued to show a wide variety of solutions for the track of Matthew. The two models have grown closer together in their solutions compared to Friday, but the GFS model showed a much greater threat to the U.S. In their 11 am EDT Saturday Wind Probability Forecast, NHC gave highest odds of tropical storm-force winds in the U.S. to West Palm Beach, Florida (24%).

Longer-range track forecast for Matthew: the U.S. East Coast at risk
Matthew will likely to punish a large portion of The Bahamas on Wednesday and Thursday. The threat to the U.S. East Coast remains highly uncertain, though, as one can see from the latest set of ensemble model runs (Figure 3). Our two best models, the GFS and European, differ considerably in their handling of the upper-level low pressure system that will be guiding Matthew northwards next week. The European model prefers a track for Matthew out to sea, while the GFS model keeps Matthew perilously close to the U.S. coast. Bolstering the GFS model’s case is the latest 00Z Saturday run of the UKMET model, which brings Matthew to a landfall in South Carolina in seven days. However, the Canadian, HWRF, and GFDL models show a track for Matthew more like the European model’s track, out to sea, so it’s anybody’s guess where Matthew will be five days from now. One wild card: an area of low pressure associated with a tropical wave has formed over the central tropical Atlantic several hundred miles east of the Lesser Antilles, and may alter the steering currents for Matthew. About 50% of the members of the European ensemble predicted that this system would develop into a tropical depression or tropical storm as it heads northwest next week; the GFS model showed virtually no development. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave this system 2-day and 5-day odds of development of 10% and 20%, respectively. If this storm develops significantly, it may exert a steering influence on Matthew that could help pull it out to sea.

Figure 4. Track forecasts from the five European model ensemble members [gray lines] that most closely match the operational run [red line] during the first 72 hours, starting at 00Z Saturday, October 1, 2016. The red line is a version of the 00Z Saturday operational model track that has been adjusted and calibrated using a proprietary technique to account for systemic model errors. Only one of these forecasts showed Matthew hitting the U.S. Image credit: Climate Forecast Applications Network (CFAN).

Bob will be back this afternoon with an update on Matthew. Wunderblogger Steve Gregory posted a Saturday afternoon update on Matthew, CAT 4 HURRICANE MATTHEW: THREAT TO US CONTINUES.

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.