Tropical Storm Matthew Gains Strength in the Eastern Caribbean

Matthew continued its westward trek on Thursday away from the Lesser Antilles and into the Caribbean. As of 11am Thursday, the storm had maximum sustained winds of 70mph and a minimum central pressure down to 996mb. Matthew’s forward speed had slowed a bit since its first advisory on Wednesday, but it was still moving at 15mph. Tropical Storm Watches were up for the Netherland Antilles (Aruba, Bonaire, and Curacao).

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The forecasted path of Matthew is rather certain for the next couple of days. Thanks to a large ridge to its north, the storm will continue moving to the west, albeit gradually slowing down at the same time. However, a digging trough across the east coast this weekend will sharply turn the storm to the north. While the models disagree on the timing of this turn, they all feature it at some point. The official forecast from the NHC has Matthew making a turn to the northwest on Saturday, and northward by Sunday. The intensity forecast from NHC has the storm strengthening to a hurricane by Friday, and peaking at Category 2 strength on Monday before landfall on the eastern edge of Cuba Tuesday.

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Matthew is a rather large storm, with tropical storm force winds extending outward up to 205 miles from the center. Tropical rains continued to drench the islands of the Lesser Antilles on Thursday morning despite the storm being several hundred miles west of them. In fact, showers from the storm extended as far north as the northern Lesser Antilles all the way south to the northern coast of South America. However, enhanced satellite imagery still showed a sheared storm. Moderate to at times high wind southwesterly wind shear has continued to push the convection to the east of the center of circulation, exposing the low-level swirl.

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While wind shear is currently high enough to keep Matthew from organizing too much, it is expected to drop in the next couple of days. Models still differ on just how much it will slacken, but even if it drops off marginally, this should allow for Matthew to strengthen this weekend. The maps below depict the GFS wind shear forecast from Thursday morning (top image) to Saturday (bottom image). The lower wind shear will likely stick around through the weekend, allowing for more strengthening of the storm.

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In addition to lower wind shear, Matthew is moving into an area of extremely warm waters. Sea surface temperatures are in the mid 80s and even running a few degrees above the climatological averages.

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While the warm waters and lower wind shear will certainly help Matthew strengthen, one environmental factor working against it is the amount of moisture in the atmosphere. Water vapor imagery shows an area of drier air just to the west of the current location of the storm. It’s not dry enough to choke off Matthew but it may ultimately limit the short-term strengthening of the storm (before this weekend).

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Spaghetti plots show most of the models (statistical, dynamical, and consensus) depict a sharp turn to the north this weekend, though they differ significantly on the timing of that turn and the ultimate intensity of Matthew. It is possible that the storm will have ‘2’ periods of peak intensity – one before landfall or interaction with Cuba/Hispaniola and another after the storm emerges into the Atlantic near the Bahamas.

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Two of the major models we look at for forecasting track and intensity of tropical storms are the GFS and ECMWF (Euro). While both models show a turn northward, the GFS shows it about a day earlier. The ECMWF is also a bit farther east. By the middle of next week, the differences are really highlighted with the GFS showing a storm nearing the East Coast of the US while the Euro is farther south and east with a strengthening storm in the Bahamas. It is interesting to note that the last hurricane to make US landfall north of Florida in October was Hazel in 1954 (Sandy was post-tropical). While it still is more than a week away from any potential US impact, it is worth noting that the forecasted track of Matthew does somewhat mirror that of Hazel.

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