Matthew Dumping Extreme Rains; Threat to Southeast U.S. Growing [View all]

[malaise]

https://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3460
<snip>
Beyond The Bahamas: landfall threat for Southeast U.S. increasing
A significant westward shift in computer model guidance on Hurricane Matthew has occurred, and this could have 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 is that, for the first time in Matthew’s life, all four members of the Euro “high-probability” cluster--the members that most closely match the operational run--depict Matthew making landfall on Florida’s East Coast. (The 12Z Monday run of the NAM model also depicts the stronger ridge and suggests a Florida landfall, but the NAM is not designed to handle tropical cyclones and should be avoided for hurricane prediction, unless perhaps you’re Bart Simpson.)

Lending further credence to the westward shift are the latest 12Z Monday operational runs of our other two top track models, the GFS and UKMET. The 12Z UKMET brings Matthew into the East Coast of Florida, while the GFS brings 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 several previous operational GFS runs had suggested that a Southeast landfall would be limited to the NC Outer Banks at most. Likewise, the 12Z Monday GFS ensembles (GEFS) now include a majority of runs making landfall somewhere between Florida and North Carolina, a major shift west from previous GFS ensembles. In addition, the 12Z Monday run of the HWRF model is tracking about 1 degree (roughly 60 miles) west of its previous two runs, now showing a potential landfall in eastern North Carolina by late Friday.


In our next update this evening, we’ll look at results from the 12Z Euro and GFS ensemble runs and the 12Z Euro operational run. For now, it’s important to keep in mind that the uncertainty “cones” produced by NHC are not tailored specifically for a given hurricane: they are based on the average error in NHC forecasts over the preceding five years. On average, about two-thirds of all hurricanes stay within the cone, but some hurricanes are tougher to predict than others. Given the wide range of model guidance on Matthew, and the recent westward shift, the actual uncertainty for this hurricane may be wider than the 120-hour cone location implies. In any event, there is enough model support for various possibilities that people all the way from Florida to Maine should continue to take seriously the possibility of impacts from Matthew. As always, the NHC is the place to turn for official 5-day forecasts, including intensity and track guidance and cones of uncertainty.

------------------------
Al Roker in on GEM$NBComcast discussing Matthew