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A growing threat for the Southeast U.S.
A significant westward shift unfolded Monday in computer model guidance on Hurricane Matthew, and this has big implications for the hurricane’s potential impact on the U.S. East Coast. The main reason appears to be stronger ridging south of 98L and north of Matthew than earlier predicted, which may help to nudge Matthew far enough west for major impacts along the Southeast U.S. coast. Last night’s 50 ensemble runs from the 00Z Monday European model included a number of tracks making landfall along the U.S. East Coast. Most concerning was that all four members of the Euro “high-probability” cluster--the members that most closely match the operational run--depicted Matthew making landfall on Florida’s East Coast. Today’s 12Z Monday Euro ensemble continued along the same lines (see Figure 4 below).

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 12Z (8:00 am EDT) Monday, October 3, 2016. The red line is a version of the 12Z Monday operational model track that has been adjusted and calibrated using a proprietary technique to account for systemic model errors. The high-probability cluster (grey lines) perform better than other ensemble members at forecast times of five days and beyond. Image credit: Climate Forecast Applications Network (CFAN).


A track mirroring the Southeast coastline?
Other models have now moved into the Euro ensemble’s camp. The 12Z and 18Z GFS brought Matthew considerably closer to the Florida coast than earlier runs, with a projected landfall in northern South Carolina this weekend (see Figure 4 below) and a second landfall on Cape Cod less than 36 hours later. The 18Z GFS nudged Matthew’s track so that it arrives very near the central Florida coast on Thursday night, then hugs the coast all the way to Cape Hatteras, North Carolina, on Sunday morning. The 12Z and 18Z Monday GFS ensembles (GEFS) featured a majority of runs making landfall somewhere between Florida and North Carolina, a major shift west from previous GFS ensembles. The 12Z Monday run of the HWRF model tracked about 1 degree (roughly 60 miles) west of its previous two runs, now showing a potential landfall in eastern North Carolina by late Friday.

Obviously, a direct landfall from Matthew could inflict a devastating blow. The key variable in Matthew’s track later this week is how far north and west the hurricane moves before it begins the expected northeastward motion that will take it toward the Northeast U.S. and Canadian Maritimes. A gradual, arcing turn near the coast, as depicted in the 18Z GFS, would avoid a perpendicular, head-on landfall (the type that occured in New Jersey with Hurricane/Superstorm Sandy). This would act to reduce the intensity of storm surge at any given point. Such a track would also keep the mainland primarily on the less-intense western side of Matthew. On the other hand, such a track would bring hurricane-related impacts, including strong winds and heavy rains, to many millions of coastal residents. One particular concern is the risk of very heavy rain from eastern North Carolina into the Delmarva region. The last two weeks have already left totals exceeding 10” in some areas (see Figure 6 below). Any rains from Matthew would fall atop saturated soil, and even strong tropical-storm-force winds could lead to widespread tree uprooting. We can also expect major beach erosion as Matthew churns northeastward.

The governors of Florida and North Carolina have already declared states of emergency for all of FL and parts of central and eastern NC.

Far too many hurricanes come across Florida from all directions to ever make me want to live there.

Be Safe. If you need to haul azz to SC let me know.


Dan