[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 211748
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI MAR 21 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
SECTIONS OF SOUTH AMERICA...AND THE ATLANTIC OCEAN TO THE
AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING
INFORMATION IS BASED ON SATELLITE IMAGERY...METEOROLOGICAL
ANALYSIS...WEATHER OBSERVATIONS...AND RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...THE ITCZ...

ITCZ AXIS IS CENTERED ALONG 7N12W 3N17W CROSSING THE EQUATOR AT
27W THEN TO 3S41W. SCATTERED MODERATE CONVECTION WAS OCCURRING
THIS MORNING WITHIN 150 NM EITHER SIDE OF A LINE EXTENDING FROM
4N29W TO 3S7E.

...DISCUSSION...

GULF OF MEXICO...

A RELATIVELY FLAT...MID- TO UPPER-LEVEL TROUGH OVER THE WRN
ATLANTIC HAS DRAGGED AN ASSOCIATED COLD FRONT TO A POSITION FROM
THE STRAITS OF FLORIDA TO THE NE TIP OF THE YUCATAN. THE FRONT
LINKS UP WITH A WEAK 1016MB SURFACE LOW MIDWAY BETWEEN MERIDA
AND COZUMEL AND THEN CONTINUES SWD TO NEAR 14.5N88.5W. WITH
LITTLE AMPLITUDE TO THE WRN ATLANTIC TROUGH AND A REASONABLY
STRONG MID-LEVEL RIDGE HOLDING SWAY OVER THE NORTHERN CARIBBEAN
...THE FRONT HAS PREDICTABLY BECOME STATIONARY. MULTI-CHANNEL
MICROWAVE IMAGERY INDICATES PRECIPITABLE WATER VALUES OF 1.5
TO 1.75 INCHES NEAR...REFLECTING A MOISTURE-RICH AIR MASS WHICH
IS ASCENDING THE BOUNDARY. THE OVERRUNNING PATTERN IS RESULTING
IN SCATTERED TO OCCASIONALLY BROKEN LOW- TO MID-LEVEL CLOUDS
COVERING MUCH OF THE SERN AND S CENTRAL GULF OF MEXICO...WITH
DENSE LOW CLOUDS ALSO COVERING MUCH OF THE YUCATAN AND THE
HIGHER TERRAIN OF CENTRAL AMERICA.  OTHER THAN THE LOW- TO
MID-LEVEL CLOUDS...FORCING MECHANISMS REMAIN FAIRLY WEAK AND
THUS THE ONLY CONVECTION TO SPEAK OF IS SPROUTING EARLY WITHIN
ABOUT 60 NM S OF 23N BETWEEN 85W AND 87W EARLY THIS AFTERNOON.
ELSEWHERE...A SHALLOW STRATOCUMULUS DECK OF CLOUDS IS VEILED
ACROSS THE NW AND N CENTRAL GULF BUT CLEAR SKIES COVER THE NE
AND SW GULF UNDER THE INFLUENCE OF WEAK HIGH PRESSURE.

A MORNING QUIKSCAT PASS REVEALS A GENERALLY LIGHT WIND REGIME
NORTH OF THE FRONT...WITH WINDS N TO NE WINDS OF 10 TO 15 KT
EXCEPT 20 TO OCCASIONALLY 25 KT E OF 90W WHERE THE PRESSURE
GRADIENT IS STRONGER.  BUOY...CMAN...AND SHIP REPORTS INDICATE 5
TO 8 FT SEAS IN N E SWELL COVERING THE SOUTHER HALF OF THE
GULF...WHILE 2 TO 5 FT SEAS ARE THE RULE N OF ABOUT 26N.

MODEL GUIDANCE DEPICTS AN ILL-DEFINED...SRN STREAM SHORTWAVE
RACING ACROSS THE GULF LATE TONIGHT AND SAT..WHICH SHOULD LEAD
TO A GENERAL RETREAT OF THE STATIONARY FRONT ACROSS THE EXTREME
SERN GULF AND FL.  AS THIS OCCURS...A WEAK SURFACE WAVE IS
FORECAST TO FORM ALONG THE FRONT AND REACH THE W COAST OF FL SAT
AFTERNOON.  AS THE SURFACE WAVE DARTS NE INTO THE WRN ATLANTIC
SAT NIGHT...EXPECT THE BOUNDARY TO RETURN ACROSS FL AND THE GULF
EARLY SUN...FOLLOWED BY A SECOND REINFORCING SHOT OF COOLER AND
DRIER AIR SUN.

CARIBBEAN SEA...
A STRONG MID- TO UPPER-LEVEL LIES DIRECTLY N HISPANIOLA AND
PUERTO RICO AND SHOULD PREVAIL ACROSS THE CARIBBEAN BASIN
THROUGH AT LEAST EARLY THIS WEEKEND.  THE RIDGE...WHICH HAS
DOMINATED THE REGION FOR MUCH OF THIS WEEK...CONTINUES TO FAVOR
BROAD SUBSIDENCE AND A LACK OF CONVECTIVE CLOUDS...ESPECIALLY E
OF 80W.  IN FACT...WATER VAPOR IMAGERY INDICATES THE STRONGEST
SUBSIDENCE IS CENTERED FROM E OF THE LESSER ANTILLES TO ABOUT
75W. HOWEVER...MODELS SUGGEST THAT THE INFLUENCE OF THIS FEATURE
SHOULD DIMINISH LATER THIS WEEKEND...AS A BROAD TROUGH DIGGING
OVER THE ERN CONUS REACHES DEEP INTO THE WRN CARIBBEAN.
OTHERWISE...THERE IS STILL EVIDENCE OF WHAT WAS A RARE FRONTAL
PASSAGE OVER THE NE CARIBBEAN AND LESSER ANTILLES EARLIER THIS
WEEK...WITH PATCHY STRATOCUMULUS CLOUDS INTERSPERSED WITH DEEPER
CUMULUS.  THE MOST RECENT SOUNDING FROM SAN JUAN STILL REVEALS A
TRADE WIND INVERSION WHICH IS ATYPICALLY HIGH AT ROUGHLY 750
MB.  IN ADDITION...DEWPOINTS FROM ABOUT MARTINIQUE NWWD THROUGH
PUERTO RICO REMAIN IN THE 60S...REPRESENTING A SLOW RECOVERY
FROM WHAT THEY WERE JUST A FEW DAYS AGO.

W OF 80W...THE STATIONARY FRONT OVER THE GULF EXTENDS SWD ALONG
BUT OFFSHORE THE YUCATAN AND BELIZE COASTS...WITH AN EXTENSION
INTO THE MORE MOUNTAINOUS TERRAIN OF CENTRAL AMERICA. WHERE
LOW-LEVEL NWLY FLOW MEETS THE TRADES...WIDESPREAD CLOUDINESS IS
NOTED NEAR AND ALONG THE FRONT OVER THE WRN GULF OF HONDURAS
WITH LITTLE IN THE WAY OF ANY ORGANIZED PRECIPITATION.  VISIBLE
SATELLITE IMAGERY ALSO INDICATED A WEAK LOW-LEVEL CYCLONIC
CIRCULATION IMMEDIATELY AHEAD OF THE FRONT OVER THE CENTRAL GULF
OF HONDURAS.  HOWEVER...A QUIKSCAT PASS FROM EARLIER SUGGESTED
THAT THE CIRCULATION IS ABOVE THE SURFACE LAYER.

FINALLY...LONG PERIOD NE SWELL CONTINUES TO ARRIVE PRIMARILY
OVER THE CARIBBEAN...WITH A MIX OF BUOYS AND SHIPS INDICATING 10
TO 14 FT WAVE HEIGHTS STILL OVER THE AREA E OF 65W. ONLY A
GRADUAL DIMINUTION IN WAVE HEIGHT IS EXPECTED DURING THE NEXT
24 HOURS.

ATLANTIC...
THE SAME COLD FRONT OVER THE GULF EXTEND NEWD THROUGH THE
CENTRAL BAHAMAS ALONG A LINE RUNNING FROM 24N80W TO 26N70W TO
31N59W AS OF 1500 UTC....WITH THE FRONT STATIONARY W OF ABOUT
70W. OVERRUNNING MOISTURE ALONG THE BOUNDARY HAS CAUSED THE
DEVELOPMENT OF A BAND OF SOLID...LOW- TO MID-LEVEL CLOUDS WITHIN
90 NM NORTH OF THE FRONT...POSSIBLY MIXED WITH LIGHT SHOWER
ACTIVITY.  HOWEVER...AS WAS THE CASE IN THE GULF...LIFT ALONG
THE FRONT IS WEAKER THAN YESTERDAY...AND THERE IS NO ORGANIZED
IMPULSE ALOFT TO SUSTAIN ANYTHING MORE THAN SHOWERS AND CLOUDS.
E OF THE BOUNDARY...A 1022 MB LOW-LEVEL RIDGE IS CENTERED NEAR
24N65W AND IS MOVING SLOWLY E...KEEPING FAIRLY TRANQUIL
CONDITIONS IN PLACE.  A 1014 UTC QUIKSCAT PASS STILL INDICATED
SWLY 20 TO 25 KT WITHIN ABOUT 300 NM E OF THE FRONT...MOSTLY N
OF 30N.

ELSEWHERE...A DEEP CLOSED CYCLONE N OF THE AREA NEAR 36N40W IS
CARRYING A SLOW-MOVING COLD FRONT FROM 31N32W TO 16N52W.  THIS
SYSTEM IS THE SAME STORM...WHICH DEEPENED TO ABOUT 965MB LATE
THIS PAST WEEKEND/EARLY THIS WEEK AND PRODUCED AN IMPRESSIVE NW
TO N SWELL OVER THE WRN ATLANTIC.  THIS SWELL CONTINUES TO
PROPAGATE FROM ITS SOURCE REGION AND HAS NOW ENVELOPED THE
BETTER PART OF THE TROPICAL ATLANTIC.  IN FACT...10 TO 15 FT
WAVES IN A NW SWELL COVER THE AREA S OF 31N AND E OF 60W.  ALL
OF THE ASSOCIATED OVERRUNNING CLOUDS AND PRECIPITATION LIE NORTH
AND EAST OF THE AREA...WITH ONLY SPOTTY LOW CLOUDS IN THE FRONTS
WAKE.

$$
KIMBERLAIN


This weather bulletin was brought to you by:
www.nashvilleweather.net