Post-Tropical Cyclone Bill Discussion Number 7
NWS National Hurricane Center Miami FL AL022021
1100 PM AST Tue Jun 15 2021
Satellite imagery indicates that Bill has become extratropical over
the north Atlantic. A partial scatterometer overpass showed 35-40
kt winds to the east-southeast of the center, so the initial
intensity is lowered to a possibly generous 45 kt. The
extratropical low should continue to weaken and move quickly toward
the northeast until it weakens to a trough between 12-24 h.
This is the last advisory on Bill by the National Hurricane Center.
Additional information on this system can be found in High Seas
Forecasts issued by the National Weather Service, under AWIPS
header NFDHSFAT1, WMO header FZNT01 KWBC, and online at
ocean.weather.gov/shtml/NFDHSFAT1.php
Tropical Storm Bill Discussion Number 3
NWS National Hurricane Center Miami FL AL022021
1100 PM AST Mon Jun 14 2021
Deep convection has increased in a cluster to the northeast of the
estimated center. Scatterometer measurements showed a couple of
40-41 kt vectors over the southeastern quadrant of the cyclone. On
this basis, the estimated intensity is increased to 40 kt, which
makes this the second tropical storm of the season, albeit a rather
high-latitude one. The system is in an environment of fairly
strong southwesterly shear, but the diffluent upper-level flow has
apparently contributed to some strengthening in a seemingly hostile
environment. Some additional short-term strengthening could occur
but by 36 hours, the cyclone should merge with a baroclinic zone
while approaching Newfoundland and become extratropical. This
transition is also shown by the FSU cyclone phase analyses of the
GFS model fields.
Bill is moving fairly swiftly northeastward, or 055/20 kt. The
track forecast appears to be straightforward. The flow ahead of a
large mid-tropospheric trough near the United States east coast
should accelerate the system northeastward for the next day or two,
and until the system dissipates. The NHC track forecast is similar
to the previous one and not far from the model consensus.
SUBJ/TROPICAL CYCLONE FORMATION ALERT (93L)//
WTNT21 KNGU 141200
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
100 NM EITHER SIDE OF A LINE FROM 32.8N 76.1W TO 35.7N 73.2W
WITHIN THE NEXT 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
WINDS IN THE AREA ARE ESTIMATED TO BE 20 TO 25 KNOTS. METSAT
IMAGERY AT 140600Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 32.7N 76.1W. THE SYSTEM IS MOVING NORTHEASTWARD AT 9 KNOTS.
2. REMARKS: MOREHEAD CITY, NC DOPPLER RADAR AND MARINE SURFACE
OBSERVATIONS INDICATE THAT A SMALL, WELL DEFINED LOW PRESSURE
SYSTEM HAS FORMED ABOUT 120 NM SOUTH OF CAPE HATTERAS, NC. SURFACE
WINDS IN STRONG THUNDERSTORMS WELL OFFSHORE AND EAST OF THE
CIRCULATION CENTER ARE SOUTHEASTERLY AT 26-28 KT WITH HIGHER GUSTS.
ENVIRONMENTAL CONDITIONS ARE ONLY MARGINALLY CONDUCIVE FOR FURTHER
DEVELOPMENT. HOWEVER, IF CONVECTIVE TRENDS CONTINUE TO IMPROVE, A
SHORT LIVED DEPRESSION OR TROPICAL STORM COULD FORM TODAY OR TONIGHT
AS THE SYSTEM MOVES NORTHEASTWARD, WELL OFFSHORE OFF THE
MID-ATLANTIC COAST.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR
CANCELLED BY 151200Z.//
BT
#0001
NNNN
1. Satellite, radar and surface observations indicate that a
well-defined low pressure system located about 90 miles southeast of
Cape Hatteras, North Carolina, is acquiring more tropical
characteristics. Environmental conditions appear conducive for
further development, and a tropical depression or tropical storm is
likely to form later today or tonight. This system is expected to
move northeastward away from the United States and move over colder
waters south of Nova Scotia on Wednesday, ending any opportunity for
further development by midweek.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...70 percent.
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