2. A surface trough interacting with an upper-level low is producing a
broad area of disorganized showers and thunderstorms about 600 miles
east-southeast of the Georgia coast. Surface pressures remain high
across the area, and significant development of this system is not
anticipated due to dry air and unfavorable upper-level winds. The
disturbance is expected to move westward today, and then
west-northwestward at about 15 mph on Monday, reaching the coast of
the southeastern United States by late Monday.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...low...20 percent.
1. Satellite imagery and nearby buoy and ship observations indicate
that a small low pressure system has formed about 500 miles
east-southeast of the Georgia-South Carolina border. Surface
pressures have begun to fall across the area, and showers and
thunderstorms have recently become better organized. Some additional
development of this system will be possible later today, and
especially on Monday when the system will move across the warmer
waters of the Gulf Stream, and a tropical depression could form
before the system makes landfall along the southern U.S. coast. The
low is expected to move westward today, and then west-northwestward
at about 15 mph on Monday, reaching the coast of the southeastern
United States by late Monday. An Air Force Reserve Unit
reconnaissance aircraft is scheduled to investigate the system
Monday afternoon, if necessary.
* Formation chance through 48 hours...medium...50 percent.
* Formation chance through 5 days...medium...50 percent.
WTNT21 KNGU 271800
SUBJ/TROPICAL CYCLONE FORMATION ALERT (96L) REISSUED //
REF/A/FLEWEACEN NORFOLK VA/271900Z JUN 21//
AMPN/REF IS TROPICAL CYCLONE FORMATION ALERT (WTNT21 KNGU 271900)//
RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
100 NM EITHER SIDE OF A LINE FROM 29.8N 72.8W TO 30.9N 78.3W
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 30 TO 40 KNOTS. METSAT
IMAGERY AT 271700Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 29.8N 72.8W. THE SYSTEM IS MOVING WEST-NORTHWESTWARD AT 12
KNOTS.
2. REMARKS: MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 30 TO 40 KNOTS.
MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 993 MB. THE
POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE
WITHIN THE NEXT 24 HOURS IS HIGH. THIS SUPERSEDES REF A.
VISIBLE SATELLITE IMAGERY AND A RECENT LOW-EARTH ORBITING
SATELLITE MICROWAVE IMAGE INDICATE THAT A SMALL SURFACE
CIRCULATION HAS FORMED BENEATH THE INCREASING THUNDERSTORM
ACTIVITY A LITTLE LESS THAN 500 NM EAST-SOUTHEAST OF THE GEORGIA-
SOUTH CAROLINA BORDER. ENVIORNMENTAL CONDITIONS ARE CONDUCIVE FOR
FURTHER DEVELOPMENT OF THE SYSTEM DURING THE NEXT 24 HOURS AND A
TROPICAL DEPRESSION IS LIKELY TO FORM WITHIN THE NEXT 24 HOURS AS
IT CONTINUES TO MOVE WEST-NORTHWESTWARD AT ABOUT 12 KT TOWARD THE
SOUTHEAST COAST OF THE UNITED STATES.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 281800Z.
//
1. A well-defined low pressure system located about 190 miles
east-southeast of Hilton Head Island, South Carolina, is producing a
large area of showers and thunderstorms mainly west of the center.
However, any additional increase in organization of the thunderstorm
activity would result in the issuance of advisories for a tropical
depression or tropical storm later this morning or afternoon. The
low is forecast to move west-northwestward at 15 to 20 mph, and the
system should reach the coast of southern South Carolina or Georgia
by this evening. If advisories are initiated, then tropical storm
warnings could be required for a portion of the Georgia and South
Carolina coasts with short notice. Regardless of development, a few
inches of rain are possible along the immediate coasts of Georgia
and southern South Carolina through Tuesday. An Air Force Reserve
Unit reconnaissance aircraft is scheduled to investigate the system
this afternoon.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...70 percent.
1. A well-defined low pressure system located about 190 miles
east-southeast of Hilton Head Island, South Carolina, is producing a
large area of showers and thunderstorms mainly west of the center.
However, any additional increase in organization of the thunderstorm
activity would result in the issuance of advisories for a tropical
depression or tropical storm later this morning or afternoon. The
low is forecast to move west-northwestward at 15 to 20 mph, and the
system should reach the coast of southern South Carolina or Georgia
by this evening. If advisories are initiated, then tropical storm
warnings could be required for a portion of the Georgia and South
Carolina coasts with short notice. Regardless of development, a few
inches of rain are possible along the immediate coasts of Georgia
and southern South Carolina through Tuesday. An Air Force Reserve
Unit reconnaissance aircraft is scheduled to investigate the system
this afternoon.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...70 percent.
Tropical Depression Four Discussion Number 1
NWS National Hurricane Center Miami FL AL042021
1100 AM EDT Mon Jun 28 2021
The area of disturbed weather and associated low pressure system
that the NHC has been tracking the past couple of days has developed
into a tropical depression off the coast of South Carolina this
morning. The inner-core cloud structure noted in high-resolution
visible satellite imagery has continued to tighten up and deep
convection with cloud top temperatures of -60 deg C have persisted
northwest through southwest of the center, yielding a Dvorak shear
pattern intensity estimate of 30 kt. This intensity estimate is
consistent with overnight scatterometer surface wind data of 31-32
kt just north of the well-defined center.
The initial motion estimate is 300/14 kt. The small tropical cyclone
is expected to maintain a west-northwestward to northwestward motion
for the next couple of days, resulting in landfall along the
south-central coast of South Carolina later this evening. The small
cyclone is expected to dissipate by 48 hours, if not sooner, when
the system will be located over the southern Appalachian Mountains.
The NHC track forecast lies close to the tightly packed GFS- and
ECMWF-based Beta-Advection models due to the lack of any significant
inner-core convection, which is allowing the cyclone to be steered
more by the low-level flow rather than the deep-layer flow as
depicted by the global and regional models.
There is a narrow window of opportunity this afternoon for the
depression to strengthen into a tropical storm before landfall
occurs. During the next few hours, the small cyclone will be passing
over the warmer Gulf Stream where sea-surface temperatures are
around 28 deg C. In addition, as the outer wind field begins to
interact with land, low-level frictional convergence along and just
offshore should help to generate deep convection just prior to
landfall, helping to spin up the wind field. The NHC forecast shows
the system becoming a tropical storm before landfall, and as a
result a tropical storm warning has been issued for a portion of
the South Carolina coast.
An Air Force Reserve Unit reconnaissance aircraft will investigate
the system this afternoon beginning around 1800 UTC, providing more
detailed information on the cyclone's intensity.
Key Messages:
1. Heavy rainfall is possible from coastal southern South Carolina
and Georgia, inland across the Piedmont of Georgia into northeast
Alabama. Isolated flooding is possible across urban areas of the
southern South Carolina and Georgia coasts.
2. Tropical-storm-force winds are expected across portions of
the South Carolina coast late this afternoon and tonight where a
Tropical Storm Warning is in effect.
3. Swells generated by the depression are expected to affect
portions of the South Carolina coast this afternoon and tonight.
These swells could cause life-threatening surf and rip currents.
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