By: Jeff Masters , 3:00 PM GMT on September 30, 2016 From Weather Underground

Hurricane Matthew put on an impressive and unexpected display of rapid intensification overnight, becoming the Caribbean’s first major hurricane since Sandy of 2012. An Air Force hurricane hunter aircraft was in Matthew on Friday morning, and between 7 am and 10 am EDT found that Matthew’s winds continued to rise and the pressure to fall. Surface winds measured by their stepped frequency microwave radiometer (SFMR) were as high as 114 mph, and flight-level winds at 10,000 feet hit 118 mph, putting Matthew at minimal Category 3 strength. Between 7 am and 10 am, Matthew’s central pressure fell 3 mb, to 968 mb.

Figure 1. Latest satellite image of Matthew.

Matthew’s rapid intensification was something of a surprise, as it occurred despite the presence of strong upper-level winds out of the southwest that were creating high wind shear of 20 knots. The intensity models generally failed to predict the rapid intensification, though the SHIPS model did give a 38% chance last night that we would see the observed amount of intensification that has occurred.

Figure 2. Curacao radar at 7:30 am EDT September 30, 2016 showed that Matthew had a well-formed eye and had spiral bands that were bringing heavy rains to the northern coast of South America. Plenty of lightning (black squiggles) was observed in the western eyewall and in region of heavy thunderstorms well to the east of the center. At this time, Matthew was a Category 2 storm with 105 mph winds. Image credit: Meteorological Department of Curacao.

Satellite loops on Friday morning showed an eye that was intermittently visible. At upper levels, high cirrus clouds streaming to the north of Matthew showed the presence of a powerful outflow channel, which was helping ventilate the storm and allowing it to intensify in the face of the high wind shear. There was little evidence of a second outflow channel becoming established to Matthew’s south, which one can see in the latest Upper Level Winds analysis from the University of Wisconsin CIMSS group. If this second outflow channel becomes well-established, continued intensification of Matthew becomes more likely. Aiding development today were warm ocean waters of 29°C (84°F) and 60 – 65% relative humidity at mid-levels of the atmosphere, as analyzed by the SHIPS model.
Figure 3. Enhanced infrared satellite image of Matthew as of 1345Z (9:45 am EDT) Friday, September 30, 2016. A eye at Matthew’s center is partially enclosed by the satellite signal of the most intense thunderstorms.

Three-day forecast for Matthew
Matthew will continue west-southwest to west through Saturday, slowing down from a forward speed of 14 mph on Friday morning to 7 mph by Saturday morning. The core of the storm will make its closest approach to northern Venezuela and northern Colombia on Friday night. This region will be on the weak (left) side of the storm, and will likely escape receiving tropical storm winds, though rains of 2 – 4” can be expected. 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 Saturday evening. Intensification by Matthew into a strong Category 3 hurricane by Sunday may occur due to the declining shear, though none of our top three intensity models—the HWRF, LGEM, and SHIPS models—were predicting on Friday morning that Matthew would achieve Category 4 strength over the coming five days. The SHIPS model gave Matthew a 32% chance of becoming a Category 4 storm by Saturday, and a 12% chance of intensifying into a Category 5 storm by Sunday.
Figure 4. This morning’s forecasts had the advantage of assimilating data from a mission flown Thursday night by NOAA’s Gulfstream-IV jet. This aircraft, nicknamed “Gonzo”, released a series of 29 dropsondes that fell on parachutes and radioed back information on temperature, pressure, humidity, and winds as they fell from the 45,000 flying altitude of Gonzo. Data from these sorts of missions can improve hurricane track forecasts by as much as 20%. It’s good to have “Gonzo” back, as it was down for extended maintenance in late August and early September due to a corrosion problem, and was not available at all during Hurricane Hermine. Image credit: NOAA/AOML/Hurricane Research Division.

Longer-range forecast for Matthew: Miami in the cone of uncertainty
Major differences continue in the longer-range model forecasts for Matthew, though the differences between our two best models—the GFS and European model—have shrunk since Thursday’s runs. This may be because of dropsonde data taken by the NOAA jet on Thursday evening, which was ingested into the 00Z Friday runs of the models. A large upper-level low pressure system over east-central U.S. will begin pulling Matthew sharply to the northwest by Sunday, but the exact timing of the turn is in doubt, resulting in major model differences in Matthew’s track. An earlier turn and faster northward motion is being predicted by the GFS model, with a landfall by the storm in Jamaica on Monday morning. The European model has Matthew heading northwards about half a day later than the GFS model, with a landfall in southwest Haiti on Monday night. As one can see from the latest set of ensemble model runs (Figure 5), the long-range uncertainties in Matthew’s long-range track are high. The tight clustering of the GFS model ensembles is quite striking compared to the spaghetti-like appearance of the European model ensembles. The differences between the Euro and GFS, and the large spread within the Euro ensemble, are perhaps not too surprising, since a slower motion for Matthew means the anticipated steering currents are weak, making them more prone to random variations. However, the persistent tight clustering of the GFS ensembles is a bit suspicious, suggesting that the model may have some sort of systematic error in its forecast.

Figure 5. The 70 forecasts from the 00Z Friday European (ECMWF) model ensemble (top) and GFS model ensemble (bottom) continued to show a wide variety of solutions for the track of Matthew. The operational (deterministic) versions of the models, run at higher resolution, are shown in red lines. The two models have grown closer together in their solutions compared to Thursday, but the European model still shows a considerably slower track for Matthew than the GFS model.

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. If the GFS model is correct, Matthew will not punish The Bahamas for multiple days, but will instead march northwards just offshore the U.S. East Coast on Tuesday and Wednesday. However, the 00Z Friday run of the UKMET model suggests that the trough of low pressure pulling Matthew to the north will be too weak to continue doing this next week; high pressure will build in on Tuesday, forcing Matthew on a more northwesterly track through the heart of The Bahamas to a point perilously close to South Florida by Thursday. The five members of the European model ensemble that most closely match the operational run over the first 72 hours (Figure 6) have two members that go along with this idea. NHC has put the 5-day cone of uncertainty for Matthew very close to Miami, and it appears likely at this point that South Florida will experience at least the fringes of Matthew, with some heavy rains, if not a direct hit. In addition, the GFS and European ensembles suggest that Matthew could move quite close to the Outer Banks of North Carolina late next week.
Figure 6. 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 Friday, September 30, 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. Image credit: Climate Forecast Applications Network (CFAN).

We will be back this afternoon with an update on Matthew. Wunderblogger Steve Gregory posted a Friday morning update on Matthew, MATTHEW NEARS CAT 3 – EAST COAST THREAT CONTINUES.

Jeff Masters

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