[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 092359
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED APR 09 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 6N11W 2N20W EQ28W EQ40W INTO NE
BRAZIL NEAR 1N50W. NO ORGANIZED AREAS OF CONVECTION ARE NOTED
ALONG THE ITCZ.

...DISCUSSION...
GULF OF MEXICO...
A SHORTWAVE TROUGH EXITING THE EASTERN GULF LAST NIGHT HAS LEFT
BEHIND A BROAD MID- TO UPPER-LEVEL RIDGE OVER THE SOUTH CENTRAL
GULF...WITH AN AXIS ORIENTED FROM THE FL PANHANDLE THROUGH THE
ISTHMUS OF TEHUANTEPEC. THE RIDGE CURRENTLY DOMINATES MOST OF
THE REGION WITH MODERATE TO STRONG SUBSIDENCE ALOFT...WITH
THE STRONGEST DRYING NOTED IN THE VICINITY OF THE YUCATAN
PENINSULA.  HOWEVER...SATELLITE IMAGERY AND UPPER-AIR DATA SHOW
A DEEP SHORTWAVE TROUGH DIGGING FROM THE WESTERN U.S. INTO
NORTHERN MEXICO AND GRADUALLY ADVANCING E. STRONG HEIGHT FALLS
AHEAD OF THIS SYSTEM AND A STRONGLY DIFFLUENT FLOW ALOFT HAVE
ALLOWED SURFACE PRESSURES TO ABRUPTLY DROP OVER THE SOUTHERN
PLAINS THIS EVENING...RESULTING IN A STRENGTHENING RETURN FLOW
OVER THE WESTERN HALF OF THE GULF.  IN FACT...SURFACE AND OTHER
DATA SUGGEST A STEADY SE TO S FLOW OF 15 TO 20 KT AND SEAS
BUILDING TO 4 TO 6 FT W OF 90W UNDER ESSENTIALLY CLEAR SKIES.
ELSEWHERE...WEAK SURFACE RIDGING IN THE WAKE OF THE SHORTWAVE
TROUGH NOW E OF THE AREA IS MAINTAINING A WEAKER BUT GRADUALLY
INCREASING EASTERLY FLOW E OF 90W... WITH ISOLATED CONVECTIVE
CELLS BRIEFLY ERUPTING OVER THE E CENTRAL GULF.

AS THE WESTERN TROUGH ORGANIZES AND CLOSES OFF OVER THE PLAINS
LATER THIS WEEK...THE SAME MID- TO UPPER-LEVEL RIDGE NOW OVER
THE GULF SHOULD REMAIN LOCKED IN PLACE THROUGH AT LEAST FRI.
EVENTUALLY THOUGH...HEIGHTS SHOULD FALL ENOUGH TO INTRODUCE A
STRONG COLD FRONT OVER THE FAR NW WATERS LATE FRI AND EARLY
SAT...WITH THE FRONT SWEEPING THROUGH THE REMAINDER OF THE GULF
BY LATE SUN.  SCATTERED TSTMS ALONG THE FRONT SHOULD GIVE WAY TO
A STRONG NW TO N FLOW OF 20 TO PERHAPS 30 KT...WITH SEAS
BUILDING TO 7 TO 11 FT.

CARIBBEAN SEA...
THE POSITIVELY-TILTED SHORTWAVE TROUGH WHICH EXITED THE GULF
LATE YESTERDAY HAS AN EXTENSION INTO THE WESTERN CARIBBEAN
...WITH THE MAIN AXIS EXTENDING FROM 21N79W TO 14N85W THIS
EVENING.
CLOUD-TRACKED WINDS AND WATER VAPOR IMAGERY INDICATE A BROAD S
TO SW FLOW AHEAD OF THE TROUGH AXIS IS TRANSPORTING MOISTURE-
RICH AIR FROM THE SW TO THE CENTRAL CARIBBEAN.  THE AMOUNT OF
MOISTURE HAS INDEED BEEN ON THE RISE DURING THE LAST 24
HOURS...WHICH HAS HELPED LATE AFTERNOON CONVECTION TO FIRE UP
FROM COSTA RICA AND PANAMA TO NORTHERN COLOMBIA.  DESPITE THE
INCREASE IN MOISTURE AND FAVORABLE DYNAMICS AHEAD OF THE TROUGH
AXIS...LITTLE IN THE WAY OF ORGANIZED CONVECTION IS OBSERVED
OVER THE REMAINDER OF THE CARIBBEAN EXCEPT FOR SCATTERED SEA
BREEZE CONVECTION OVER CUBA AND JAMAICA. OTHERWISE...WEAK
SURFACE HIGH PRESSURE NE OF THE AREA CONTINUES TO FAVOR NEAR
CLIMATOLOGICAL TO BELOW NORMAL TRADES...WITH LITTLE MORE THAN 10
TO 15 KT OF E TO SE FLOW NOTED ACROSS THE BASIN.

EXPECT THE SHORTWAVE TROUGH CURRENTLY OVER THE WESTERN CARIBBEAN
SEA TO HEAD SLOWLY E THE NEXT FEW DAYS...DRAGGING THE PLUME OF
MOISTURE OVER THE SW AND CENTRAL CARIBBEAN WITH IT.  INCREASING
INSTABILITY E OF THE TROUGH AXIS...HIGHER MOISTURE..AND A
DIFFLUENT UPPER-LEVEL FLOW SHOULD FAVOR AT LEAST SOME MARGINAL
INCREASE IN CLOUDS AND CONVECTION OVER THE CENTRAL AND THEN
EASTERN CARIBBEAN SEA...WITH THE ACTIVITY ENDING FROM W TO E AS
A DRIER NORTHWESTERLY FLOW SETS IN BY LATE WEEK.  A REVITALIZED
SURFACE RIDGE IN THE WAKE OF THE TROUGH OVER THE SW ATLANTIC
SHOULD KEEP TRADES AT THEIR PRESENT LEVELS OR SLIGHTLY HIGHER
THROUGH LATE WEEK...FOLLOWED BY A STRONG FRONT ARRIVING OVER THE
NW CARIBBEAN LATE IN THE WEEKEND.

ATLANTIC OCEAN...
THE PREVIOUSLY MENTIONED SHORTWAVE TROUGH NOW EXTENDS FROM
31N60W TO 21N77W AND IS MOVING SLOWLY SE.  THIS FEATURE SUPPORTS
A SERIES OF WEAK SURFACE LOWS ALONG A WAVY COLD FRONT EXTENDING
FROM 29N47W TO 31N60W TO 30N70W AND SE TO 26N75W. SCATTERED...
MOSTLY LOW CLOUDS LINE THE FRONT...THOUGH ISOLATED CONVECTIVE
CELLS ARE DEVELOPING WITHIN ABOUT 150 NM E OF IT N OF 28N. LIGHT
WINDS PREVAIL EITHER SIDE OF THE FRONT...WITH A SE TO S WIND OF
10 KT E OF IT AND A NE 10 TO 15 KT FLOW BEHIND IT.  OVER THE
NEXT FEW DAYS...THE MAIN SURFACE WAVE ALONG THE FRONT NEAR
30N51W SHOULD HEAD E WHILE DRAGGING A WEAK COLD FRONT INTO THE
CENTRAL ATLANTIC EXTENDING FROM 30N41W TO 25N49W BY FRI
AFTERNOON.
HIGH PRESSURE BEHIND THE FRONT SHOULD EXPAND EASTWARD...KEEPING
FAIRLY TRANQUIL CONDITIONS IN PLACE OVER THE WESTERN ATLANTIC.
AS THE RIDGE MIGRATES EASTWARD INTO THE WEEKEND...A STRONG COLD
FRONT SHOULD SWEEP OFF THE EAST COAST OF THE U.S. LATE SAT AND
EARLY SUN...WITH A STRONG S TO SW FLOW OF 20 TO 30 KT WITHIN
ABOUT 240 NM E OF THE FRONT N OF 28N.

ELSEWHERE...DEEP-LAYERED BROAD CYCLONIC FLOW CONTINUES TO
PREVAIL OVER THE NE ATLANTIC N OF 18N E OF 60W. AT THE LEADING
EDGE OF THE CYCLONIC FLOW...A WEAK COLD FRONT FROM 31N14W TO
27N30W TO 31N44W IS DIVING SE...INTRODUCING A WEAK SURFACE RIDGE
LYING WELL N OF THE AREA. THE BROAD CYCLONIC FLOW ACROSS THE
REGION HAS LED TO WEAKER-THAN-NORMAL TRADES OVER MUCH OF THE
SUBTROPICAL AND TROPICAL ATLANTIC E OF 60W...WITH THE STRONGEST
ANOMALIES NOTED N OF 20N. OVER THE NEXT SEVERAL DAYS...THE
SURFACE RIDGE CURRENTLY WELL N OF THE AREA SHOULD BUILD
SOUTHWARD AND BRING ABOUT A GRADUAL INCREASE IN THE TRADES
ACROSS THE AREA...WITH VALUES CLOSER TO CLIMATOLOGY.

FINALLY...A NARROW MID- TO UPPER-LEVEL RIDGE EXTENDS FROM NW
AFRICA WSW TO NEAR 4N49W.  ENHANCED DEEP CONVECTION ALONG THE
ITCZ AND S OF THE RIDGE AXIS FROM THE LAST FEW DAYS HAS
DRAMATICALLY DECREASED DURING THE LAST 24 TO 48 HOURS...LIKELY A
RESULT OF THE MAIN FORCING...AN ATMOSPHERIC KELVIN
WAVE...HEADING E INTO THE INDIAN OCEAN.

$$
KIMBERLAIN


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