12Z GFS total rainfall amounts for the upcoming rain event; map courtesy tropicaltidbits, NOAA
“Matthew” has officially been born and has quickly attained tropical storm status as it heads into the Caribbean Sea. This tropical system looks like it’ll be a slow-moving and major impact type of storm for the next week to ten days or so – perhaps even reaching major hurricane status – and the eastern US has to stay on guard. Meanwhile, of more immediate concern, a significant rain event is headed to the Mid-Atlantic region during the next few days and there can be some serious flooding problems and hefty precipitation totals by the time the weekend begins; especially, in the region from southern Virginia to southern Pennsylvania which includes the entire DC metro region.
12Z GFS forecast map of 500 mb height anomalies on Friday morning with vigorous upper-level low; map courtesy tropicaltidbits, NOAA
Significant rain event for the Mid-Atlantic region
Ingredients are coming together for a significant and long-lasting rain event for much of the Mid-Atlantic region with several inches of rainfall on the table for hardest hit areas likely in the region from southern Virginia to southern Pennsylvania including the entire DC metro region where this is an especially dangerous situation. Strong low pressure in the upper atmosphere (500 mb) is dropping southward from the Great Lakes region and will end up in the Tennessee Valley where it will slow down to a halt as it gets cut off from steering currents aloft. As a result of its strength and slow movement, this vigorous upper-level low pressure system will be able to pull in copious amounts of moisture from the Atlantic Ocean over an extended period of time. The main area of concern for flooding rainfall is in the area from south-central Virginia to south-central Pennsylvania; especially, in higher elevation locations where upsloping of persistent easterly winds could enhance rainfall amounts. The 12Z GFS model forecast map features total rainfall amounts of four or five inches in parts of Virginia, Maryland, Delaware and south-central PA – this may actually be an underestimate, in my opinion, for some spots in this “bullseye” region.
Latest satellite image of Tropical Storm Matthew (circled); image courtesy University of Wisconsin/SSEC, NOAA
Tropical Storm “Matthew”
Yesterday it was “Invest 97L”…now it is officially named “Matthew” and it is likely to become quite a newsmaker over the next week to ten days. There are numerous favorable factors for “Matthew” to intensify over the next few days – perhaps even into major hurricane status – as it treks slowly westward over the warmer-than-normal waters of the Caribbean Sea.
The range of forecast tracks for TS "Matthew" by the different 12Z GFS ensemble members; map courtesy tropicaltidbits, NOAA
By late this weekend or early next week, this tropical system is likely to make a sharp right turn to the north or northwest and this shift would push it over the islands of Hispaniola or Cuba. After that, there are still a wide range of possibilities including one without any landfall in the US, but the Gulf of Mexico and eastern states should stay on guard and closely monitor “Matthew” as there could ultimately be an impact. The 12Z GFS Ensemble range of potential storm tracks would keep "Matthew" rather close to the east coast and with the expected sprawling high pressure system to the north, a turn back towards the east coast is on the table with this unfolding scenario. The European forecast model has generally been considerably slower than the NOAA GFS model with its movement of Matthew and it tends to favor a track keeping it farther from the coastline. One final note, looking back there is an analog October tropical system that comes to mind with respect to one that made a sharp right turn in the Caribbean Sea and that is Hurricane Hazel which took place in 1954. The track of Hazel included a sharp right turn in the Caribbean Sea and an eventual huge impact on the US.
Meteorologist Paul Dorian