Saturday, September 03, 2016

Extratropical Storm Hermine creeps up the coast

WTNT44 KNHC 040254

1100 PM EDT SAT SEP 03 2016

Hermine has changed little in structure since the last advisory,
with most of the deep convection situated well northeast of the
center and dry, subsiding air wrapping around the southern
semicircle.  Earlier data from an Air Force Reserve Hurricane
Hunter aircraft showed that the central pressure had risen to 998
mb, and that 55-60 kt surface winds were present about 70 n mi
northwest of the center.  Based on this, the initial intensity
remains 60 kt.

Hermine continues to move east-northeastward with the initial
motion of 075/11.  During the next 72 hours, a mid- to upper-level
trough currently moving through the northeastern United States will
move close to, and then over the top of, the post-tropical cyclone.
During this evolution, Hermine is expected to move slowly northward
and then northwestward as it makes at least a partial cyclonic loop.
While the track guidance is in fair agreement for the first 48-72
hours, there remains significant spread later in the period on how
fast the cyclone will move out to sea after it merges with the
trough.  The UKMET is very slow to move the system out, while the
ECMWF is much faster.  The GFS is between these extremes, and the
current run shows a little faster motion than the previous run.
The new forecast track is similar to the previous forecast through
72 hours, and then is somewhat faster in moving the system to the
east-northeast.  Overall, there remains low confidence in any
particular model solution, and it should be noted that the GFS and
UKMET both bring the center closer to land than the official

Little change in strength is likely tonight.  On Sunday and Monday,
the interaction with the upper-level trough is expected to provide
more favorable conditions for strengthening while the system is
over sea surface temperatures of 28C or warmer, and the dynamical
models all show some deepening during this period. Based on this,
the intensity forecast calls for Hermine to become a hurricane-force
low.  The guidance is in good agreement that the system should
slowly weaken after 48 hours, and this is indicated in the forecast
as well.


1. The slow motion and large wind field associated with Hermine will
result in a long duration of hazardous conditions along much of the
mid-Atlantic coast extending into southern New England through the
holiday weekend and into midweek.

2. Small changes in the meandering track of Hermine could result in
large differences in the impacts along the mid-Atlantic coast during
the next several days.  In addition, there could be multiple
occurrences of tropical storm conditions in some locations within
the warning area during this time.

3. Although Hermine has become a post-tropical cyclone, NHC will
continue to issue its full suite of advisory and warning products as
long as the system remains a significant threat to land areas.

4. P-surge, the model that drives the Potential Storm Surge Flooding
Graphic, is designed for a wind field typical of a tropical cyclone.
The wind field of Hermine is very poorly represented by the P-surge
model and as a result, Flooding Graphics prior to today's 11 am
EDT advisory understated the inundation risk from the Carolinas
northward.  The NWS is using the GFS ensemble system instead of
P-surge for ongoing issuances of the Potential Storm Surge Flooding
Graphic to provide a more realistic depiction of the threat.

5. The Prototype Storm Surge Watch/Warning Graphic accounts for
the current wind structure of Hermine, and therefore accurately
identifies those areas at risk for life-threatening storm surge.
This graphic will also continue to be produced for Hermine.


INIT  04/0300Z 36.5N  72.1W   60 KT  70 MPH...POST-TROPICAL
12H  04/1200Z 37.1N  71.2W   60 KT  70 MPH...POST-TROPICAL
24H  05/0000Z 37.6N  71.2W   65 KT  75 MPH...POST-TROPICAL
36H  05/1200Z 37.9N  71.5W   65 KT  75 MPH...POST-TROPICAL
48H  06/0000Z 38.3N  71.8W   65 KT  75 MPH...POST-TROPICAL
72H  07/0000Z 39.0N  71.5W   60 KT  70 MPH...POST-TROPICAL
96H  08/0000Z 40.0N  70.0W   55 KT  65 MPH...POST-TROPICAL
120H  09/0000Z 41.0N  66.5W   50 KT  60 MPH...POST-TROPICAL

Forecaster Beven
FXUS61 KCAR 040305

Area Forecast Discussion
National Weather Service Caribou ME
1105 PM EDT SAT SEP 3 2016

High pressure will remain over Maine through early next week.
Hermine is expected to remain to the south of New England
through the middle of next week.

-- Changed Discussion --

Update... A warm front will move north of Maine overnight while high pressure remains ridged across the region. An area of clouds with the warm front, most extensive across northern areas, will cross the region overnight. Generally expect partly/mostly cloudy skies across northern areas overnight, with mostly clear skies across the remainder of the forecast area. Overnight low temperatures will generally range from the mid 40s to around 50 north, to around 50 to the lower 50s Downeast. Have updated the forecast to adjust for current conditions along with expected overnight temperatures and cloud cover. Previous Discussion... For Sunday, these clouds will be out of the area and temperatures will moderate into the 70s across the area. It will be slightly cooler along the coast with a light onshore flow. Humidity will also increase slightly, but it will remain comfortably low. Hermine will not affect the area through Sunday with the exception of some high cirrus clouds towards the coast.
-- End Changed Discussion --



... Sfc ridge axis wl be extndg into CWA fm high ovr northern Atlantic early in the week. Clouds wl be on the increase fm the south Mon morning as Hermine sits and spins off the Delmarva. By 12z Monday, Hermine wl hv closed off of the mid-Atlantic with a slow drift thru the week. Med range guidance is in fairly good agreement with system thru the end of the short term. Minimal impact expected to CWA with the exception of far srn zones possibly getting into showers as weakness in ridge develops. Temps on Mon and Tue will be warmer acrs nrn zones under mosunny skies. &&


Med range guidance diverges drg the long term pd with Hermine. 12z EC mvs it quickly east to the south of Nova Scotia by Wed aftn while GEM weakens it ovr the VA Capes by the end of the week. Latest GFS is about 48 hrs behind EC in ejecting it out ovr the ocean with minimal impact on CWA. Next chc for showers acrs nrn zones wl accompany a wmfnt thru by the end of the week. Temps thru the pd wl run abv normal with u70s acrs the north and arnd 80 in the south. &&