Tropical Storm Arthur Forecast Discussion Number 6

By | May 18, 2020

Issued at 1100 PM EDT Sun May 17 2020


000
WTNT41 KNHC 180256
TCDAT1
 
Tropical Storm Arthur Discussion Number   6
NWS National Hurricane Center Miami FL       AL012020
1100 PM EDT Sun May 17 2020
 
Arthur's appearance in radar and satellite imagery has degraded
significantly since the previous advisory with very little
convective banding features present now. However, an Air Force
Reserve reconnaissance aircraft investigating the cyclone late this
afternoon and early has found maximum 850-mb flight-level winds of
46 kt in the eastern quadrant along with reliable SFMR surface wind
speeds of 36-38 kt, plus a central pressure of 1003 mb. Based on
these data, the initial intensity has been held at 40 kt for this
advisory since higher wind speeds could be present within areas of
convection north of the center that were not sampled.
 
Aircraft and satellite fixes indicate that Arthur has continued to
move north-northeastward or 020/09 kt. The cyclone is forecast to
accelerate northeastward on Monday ahead of an approaching shortwave
trough and frontal system, and remain just offshore of the North
Carolina Outer Banks. By Tuesday night, Arthur will be entering the
strong mid-latitude Westerlies, which will steer cyclone eastward
and also induce extratropical transition when the cyclone merges
with the aforementioned frontal system. The new NHC track guidance
is tightly clustered about the previous forecast track, so no
significant cross-track changes were required. However, some slight
changes to the forward were required on days 2 and 3, and the new
NHC track forecast now shows Arthur moving a little faster to the
east and southeast on those days.
 
Arthur is currently moving over the warmest waters in the Gulfstream
where ocean temperatures are 26-26.5 deg C. However, some mid-level
shear undercutting the otherwise upper-level outflow pattern,
coupled with the entrainment of dry mid-level air has disrupted the
overall convective pattern. These unfavorable conditions should
continue for the next coupe of days, with only intermittent bursts
of deep convection occuring near the center until Arthur passes
northeast of the Outer Banks by late Monday. Thereafter, baroclinic
effects along with extratropical transition are expected to cause
some further strengthening before weakening begins late Tuesday and
on Wednesday. The official intensity forecast follows a blend of the
intensity consensus model IVCN, and the GFS and ECMWF model
forecasts.
 
 
Key Messages:
 
1. A Tropical Storm Warning is in effect for a portion of the
North Carolina coast.  Tropical-storm-force winds and heavy rains
are expected there on Monday.
 
2. Dangerous coastal surf conditions and rip currents are expected
to spread northward along the southeast U.S. coast to the
mid-Atlantic states during the next couple of days.  See products
from your local National Weather Service Forecast Office for more
details.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0300Z 32.4N  76.9W   40 KT  45 MPH
 12H  18/1200Z 34.0N  75.6W   40 KT  45 MPH
 24H  19/0000Z 35.8N  73.2W   45 KT  50 MPH
 36H  19/1200Z 36.4N  70.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  20/0000Z 36.0N  67.7W   50 KT  60 MPH...POST-TROP/EXTRATROP
 60H  20/1200Z 35.0N  66.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  21/0000Z 33.8N  64.6W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  22/0000Z 31.6N  62.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  23/0000Z...DISSIPATED
 
$$
Forecaster Stewart
 

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