1:00 PM | *Hurricane Florence remains a threat to the US east coast for the mid-to-latter part of next week…the remains of Gordon to contribute to a swath of heavy rainfall in the near-term*

11AM position of Atlantic Basin tropical systems with Tropical Depression Gordon located over the south-central US, Hurricane Florence over the central Atlantic, and a third system in the eastern Atlantic; courtesy NOAA/NHC

Overview
Hurricane Florence continues to churn slowly to the northwest over the central Atlantic and it remains a threat to the US east coast.  Tropical Depression Gordon has nearly grinded to a halt over the south-central US and it will combine with a strong cool frontal system to produce a wide swath of heavy rainfall over the next several days extending from the south-central US to the Mid-Atlantic.  And if that isn’t enough, there is a third tropical wave in the eastern Atlantic that has an excellent chance of intensifying in coming days as it likely takes a more “southern” track compared to Florence.

A swath of heavy rainfall next five days partially as a result of the remains of Gordon; courtesy NOAA/WPC

Gordon
With much of the (well justified) attention going to Hurricane Florence, the impact that the remains of Gordon may have over the next several days should not be ignored.  In fact, significant rainfall is likely over the next several days from the south-central US to the Mid-Atlantic from the combination of Gordon and a frontal system. Flooding may be the result of this heavy rainfall in some areas given the well-saturated grounds in much of the eastern half of the nation.  

At 11am, Tropical Depression Gordon has nearly grinded to a halt with movement at only 5 mph to the north-northwest.  Gordon should continue drifting to the NW over the next 24 hours and then take a turn to the northeast and accelerate over the weekend from the south-central US towards the Great Lakes.  Meanwhile, a strong cool frontal boundary zone will slide southeastward over the next 24 hours and reach the southern Mid-Atlantic region before stalling out.  As Gordon pushes to the eastern Great Lakes early next week, it’ll interact with the frontal system and pull it northward as a warm front.  The combination of Gordon and the stalling out cool frontal system will result in a wide swath of heavy rainfall from the south-central US to the Mid-Atlantic region.  Occasional showers are possible here tonight as the front arrives in the I-95 corridor with embedded thunderstorms and the rain threat will continue on Friday, Saturday, Sunday and Monday - some of the rain can be heavy at times.  As strong high pressure builds to the north over the next 24-48 hours across southeastern Canada, low-level winds will turn to an east-to-northeast direction and it’ll become noticeably cooler by the weekend.  In fact, both weekend days could feature high temperatures in the lower 70’s in the DC-to-Philly-to-NYC corridor. 

00Z Euro ensemble storm tracks for Hurricane Florence with many reaching to the US east coast; courtesy weathermodels.com (Dr. Ryan Maue), ECMWF

Florence
Florence has just lost its “major” hurricane status as the max sustained winds reported at 11am have dropped slightly to 105 mph (now a category 2).  In coming days, Hurricane Florence will actually head over warmer-than-normal water in the Atlantic Ocean and this will be favorable for intensification.  Hurricane Florence poses no threat to land through the early part of next week.  

12Z GFS 500 mb height anomaly forecast map for Monday, September 10th, with a deep upper-level trough passing by to the north of Florence; courtesy NOAA/EMC, tropicaltidbits.com

Looking to later next week, however, there is still a real concern that Florence will push to the west underneath a tremendous high pressure ridge that will build across southeastern Canada and the northwest Atlantic early next week.  There will be a deep upper-level trough of low pressure pushing eastward this weekend across the north Atlantic, but it appears it will not “capture” Florence and not be able to "pull" it to the north.  Instead, it increasingly appears that Florence will be “left behind” and the building high pressure ridge to the north will allow for a westward push towards the US east coast.  Any potential impact by Florence on the US east coast by Florence would likely be during the middle or latter part of next week.  However, given the possible strong and expansive (blocking) ridge of high pressure to the north next week, the potential does exist for Florence to slow down as it approaches the east coast - never a good thing to see - perhaps it'll even stall out or end up taking some kind of a loop near or over the coast.  

12Z GFS 500 mb height anomaly forecast map for Wednesday, September 12th, with a tremendous ridge of high pressure over SE Canada/NW Atlantic as Florence "slips" underneath; courtesy NOAA/EMC, tropicaltidbits.com

System 3
Yet another tropical system trails Florence in the eastern part of the Atlantic Ocean.  This system has an excellent chance of intensifying in coming days to “named” (Helene) status and it is likely to take a more “southern” route than Florence – likely heading towards the Caribbean Sea.  In a week or so, there is a chance this system will sit over or just to the north of the Caribbean Sea and it could very well take a turn at that point to the northwest - and perhaps towards the Southeast US.

Stay tuned...a busy couple of weeks.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com 

Extended video discussion on the remains of Gordon and the continuing east coast threat from Hurricane Florence: