[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 120000
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI APR 11 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2345 UTC.

...ITCZ...
ITCZ AXIS IS CENTERED ALONG 5N8W 2N20W CROSSING THE EQUATOR NEAR
34W THEN TO NE BRAZIL NEAR 2S44W. SCATTERED MODERATE CONVECTION
IS WITHIN 90 NM EITHER SIDE OF THE AXIS BETWEEN 8W-11W. ISOLATED
CLUSTERS OF MODERATE CONVECTION ARE WITHIN 60 NM N OF THE AXIS
BETWEEN 23W AND 30W. SCATTERED MODERATE ALSO BETWEEN 1N AND 4N
BETWEEN 40W AND 50W.6W

...DISCUSSION...
GULF OF MEXICO...
AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDING FROM S FLORIDA
TO THE BAY OF CAMPECHE IS PRODUCING MODERATELY STRONG SUBSIDENCE
AND FAIR SKIES OVER MUCH OF THE SOUTHERN AND EASTERN GULF THIS
EVENING. WEAK SURFACE RIDGING NOSES INTO THE EASTERN GULF AND IS
PRODUCING E TO SE WINDS OF 10 TO 15 KT...EXCEPT 5 TO 10 KT OVER
THE FAR NE. HOWEVER...A BROAD MID- TO UPPER-LEVEL TROUGH OVER
THE CENTRAL U.S. IS BEGINNING TO DIG INTO THE EASTERN STATES...
DRIVING AN ASSOCIATED COLD FRONT INTO THE NW GULF FROM 30N93W TO
26N95W TO 23N98W AND THEN WINDING INLAND OVER NE MEXICO.
SATELLITE AND RADAR IMAGERY INDICATE THE FRONT IS PUSHING SE
WITH LITTLE FANFARE...ONLY DEFINED BY SCATTERED LOW CLOUDS BOTH
BEHIND AND AHEAD OF THE BOUNDARY.  W OF THE FRONT...N TO NE
WINDS OF 10 TO 15 KT IS DEVELOPING AS WEAK HIGH PRESSURES
BUBBLES SOUTHWARD INTO NE MEXICO...WITH TEMPERATURES 5 TO 10
DEGREES COOLER AND DEWPOINT TEMPERATURES 20 TO 30 DEGREES LOWER.

IN THE SHORT-TERM...A VIGOROUS SHORTWAVE SLIDING EASTWARD IN THE
BASE OF THE CENTRAL U.S. TROUGH SHOULD HELP PUSH THE FRONT
THROUGH THE REMAINDER OF THE GULF SAT AND SUN...ACCOMPANIED BY
BRISK NW TO N WINDS OF 20 TO 30 KT...EXCEPT TO GALE FORCE
BRIEFLY OVER THE SW GULF SUN. SEAS SHOULD QUICKLY BUILD TO 8 TO
15 FT OVER THE W GULF AND 5 TO 9 FT OVER THE EASTERN GULF...WITH
WINDS AND SEAS GRADUALLY SUBSIDING LATER ON MON.

CARIBBEAN SEA...
WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS SHOW A POSITIVELY-
TILTED MID- TO UPPER-LEVEL TROUGH PUSHING SE THROUGH THE
CARIBBEAN...LYING FROM 19N63 TO AROUND 12N77W.  A PLUME OF UPPER
TROPOSPHERIC MOISTURE BEING DRAWN NE AHEAD OF IT IS NOW CONFINED
TO FARTHER NORTHERN SOUTH AMERICA THROUGH THE WINDWARD ISLANDS
...WHILE MODERATE TO STRONG SUBSIDENCE IS EVIDENT OVER THE REST
OF THE CARIBBEAN COINCIDENT WITH THE CONVERGENT REGION W OF THE
TROUGH AXIS AND THE STRONG MID- TO UPPER-LEVEL HIGH SPILLING
FROM THE GULF INTO THE NW CARIBBEAN.  WITH LARGE-SCALE
SUBSIDENCE NOW OVERSPREADING MOST OF THE BASIN...VERY LITTLE IN
THE WAY OF CONVECTION IS NOTED EXCEPT FROM COSTA RICA TO
NORTHERN COLOMBIA AND OVER THE HIGHEST TERRAIN OF GUATEMALA AND
HONDURAS. AT THE SURFACE...LOWER HEIGHTS ALOFT HAVE RESULTED IN
A DISPLACED AND FAIRLY WEAK SURFACE RIDGE...WHICH IN TURN HAS
TRANSLATED INTO LOWER-THAN-NORMAL SURFACE PRESSURES OVER THE
ENTIRE AREA.  CONSEQUENTLY...TRADES CONTINUE TO BE RATHER WEAK
AS THEY HAVE BEEN THE LAST FEW DAYS...EXCEPT TYPICALLY HIGHER
IMMEDIATELY NW OF THE COLOMBIAN COAST AND OVER THE GULF OF
HONDURAS.  IN FACT...LIKE YESTERDAY...QUIKSCAT AND ASCAT PASSES
REVEAL E TO SE WINDS OF 20 TO POSSIBLY 25 KT.

OVER THE NEXT FEW DAYS...THE DEEP TROUGH OVER THE CENTRAL U.S.
SHOULD BARREL EASTWARD...CAUSING HEIGHTS TO COLLAPSE INTO THE
WESTERN CARIBBEAN.  THIS SHOULD ALLOW THE COLD FRONT SLIDING
THROUGH THE GULF THIS WEEKEND TO DROP AS FAR SOUTH AS AN EASTERN
CUBA-CAPE GRACIAS A DIOS NICARAGUA LINE BY EARLY TUE.  FOLLOWING
ITS PASSAGE...NW TO N WINDS OF 15 TO 20 KT SHOULD PUSH SOUTHWARD
FROM THE YUCATAN CHANNEL IN TO THE GULF OF HONDURAS...WITH SEAS
BUILDING TO 6 TO 9 FT.  WITH THE MAIN DYNAMICS WELL TO THE
N...ONLY SCATTERED SHOWERS AND PERHAPS AN ISOLATED TSTM COULD
OCCUR NEAR OR DIRECTLY AHEAD OF THE BOUNDARY. OTHERWISE...WITH
HIGH PRESSURE DISPLACED TO THE NE...LOWER-THAN-NORMAL PRESSURES
AND A WEAK GRADIENT SHOULD KEEP TRADES AT OR BELOW
CLIMATOLOGICAL AVERAGES STRAIGHT THROUGH EARLY NEXT WEEK.

ATLANTIC OCEAN...
THE WEAK POSITIVELY-TILTED SHORTWAVE TROUGH OVER THE CARIBBEAN
EXTENDS WELL TO THE NE...FROM THE NE CARIBBEAN TO AROUND 31N41W
PER WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS.  THIS FEATURE
IS CARRYING A WEAK YET COMPLEX FRONTAL SYSTEM N OF 25N BETWEEN
37W AND 60W.  MORE SPECIFICALLY...THE MAIN FRONTAL WAVE LIES N
OF THE AREA NEAR 33N41W...WITH AN ILL-DEFINED BOUNDARY EXTENDING
SW FROM 31N40W TO 27N46W THEN WESTWARD TO A SECOND BUT WEAKER
FRONTAL WAVE NEAR 27N56W. THE FRONT THEN CONTINUES SW TO NEAR
23N62W. SATELLITE IMAGERY INDICATES A BROAD AREA OF
MULTI-LAYERED CLOUDINESS...WITH A FEW EMBEDDED SHOWERS AND TSTMS
IN THE DIVERGENT REGION AHEAD OF THE TROUGH AXIS.  MOST OF THE
ACTIVITY IS LIMITED TO THE AREA N OF 20N W OF 50W...WITH THE
GREATEST CONCENTRATION WITHIN 350 NM E OF THE ASSOCIATED FRONT N
OF 27N. ALTHOUGH FAIRLY LIGHT WINDS COVER MUCH OF THE CENTRAL
AND WESTERN ATLANTIC...LOCALLY STRONGER SOUTHERLY WINDS OF 20 TO
30 KT ARE NOTED N OF 26 E OF THE FRONT.  MODELS SHOW THIS
FEATURE IN THE PROCESS OF MERGING WITH A MORE POTENT NORTHERN
STREAM SYSTEM TONIGHT AND SAT...WITH THE CONSOLIDATED SYSTEM
RACING E OF THE AREA BY SUN.  A RECONSTITUTED SURFACE RIDGE IN
ITS WAKE SHOULD MIGRATE FROM THE WESTERN TO THE CENTRAL
ATLANTIC..AS A STRONG COLD FRONT MOVES OFF THE SE U.S. COAST SUN.

ELSEWHERE...A WEAK 1026 MB SURFACE RIDGE NEAR 37N26W CURRENTLY
EXTENDS INTO THE NE ATLANTIC BUT SHOULD QUICKLY REPLACED WITH A
DEEP-LAYERED CYCLONIC FLOW THIS WEEKEND...INTRODUCED AFTER THE
PASSAGE OF THE ABOVE FRONTAL SYSTEM. A PATTERN OF DEEP-LAYERED
CYCLONIC FLOW HAS PERSISTED OVER THE EAST ATLANTIC N OF 15N E OF
60W FOR MUCH OF THE WEEK...WHICH HAS CONTINUED TO KEEP THE
STRENGTH OF THE TRADE WIND FLOW BELOW AVERAGE. WEAKER-THAN-
NORMAL TRADES AND LOWER-THAN-NORMAL SURFACE PRESSURES SHOULD
PREVAIL ACROSS THIS AREA THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK.

OTHERWISE...AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDS FROM
NW AFRICA TO JUST E OF THE LESSER ANTILLES...WITH AN AXIS
RUNNING FROM 20N07W TO 12N58W. S OF THE RIDGE AXIS...CONVECTION
REMAINS FAIRLY LIMITED...WHICH IS IN STARK CONTRAST TO THAT
OBSERVED LAST WEEK INTO EARLY THIS WEEK.  REAL-TIME NCEP
RE-ANALYSIS DATA INDICATE THAT THE RECENT INCREASE IN CONVECTIVE
ACTIVITY WAS LIKELY RELATED TO A FAST-MOVING TROPICAL CONVECTIVE
FORCING...WHICH HAS NOW MOVED E AFRICA AND THE INDIAN OCEAN.

$$
KIMBERLAIN/ECKERT




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