Wednesday Afternoon Tropical Weather Discussion

AXNT20 KNHC 041754
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED JUN 04 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND 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
1715 UTC.

...TROPICAL WAVES...

A WELL-DEFINED TROPICAL WAVE ALONG 40W S OF 20N IS MOVING W
10-15 KT...WITH A WEAK 1012 MB CIRCULATION EMBEDDED ALONG THE
AXIS NEAR 10N. ALTHOUGH THE WAVE CONTINUES TO DOMINATE A LARGE
AREA...ASSOCIATED CONVECTION HAS BEEN NOTICEABLY DECREASING
DURING THE LAST 24 HOURS. IN FACT...ALL THAT REMAINS IS A SMALL
CONVECTIVE CLUSTER IMMEDIATELY NE OF THE WEAK SFC LOW ANALYZED
10N40W. A CURSORY LOOK AT REYNOLDS WEEKLY SEA SURFACE
TEMPERATURES REVEALS THAT MOST OF THE WAVE LIES OVER A REGION
WITH SSTS LESS THAN 26.5C...WHICH IS TOO COOL TO SUSTAIN
ORGANIZED CONVECTION.

TROPICAL WAVE IS IN THE E CARIBBEAN SEA ALONG 65W/66W S OF 17N
MOVING W 10-15 KT. ALTHOUGH VISIBLE SATELLITE IMAGERY REVEALS NO
CLEAR FEATURES ASSOCIATED WITH THE WAVE...MIMIC-TPW ANIMATION
PROVES MORE HELPFUL IN SHOWING A PLUME OF ENHANCED MOISTURE
CROSSING THROUGH THE EASTERN CARIBBEAN. IN ADDITION...TIME
SERIES DATA FROM SAN JUAN AND SURROUNDING AREAS SHOW A NOTABLE
INCREASE IN LOW- TO MID-LEVEL MOISTURE AND ANOMALOUS SLY FLOW
ACROSS THE REGION IN ITS WAKE. LITTLE ASSOCIATED DEEP
CONVECTION IS NOTED IN ASSOCIATION WITH THIS FEATURE.

TROPICAL WAVE IS IN THE CARIBBEAN ALONG 81W S OF 17N MOVING W
10-15 KT. THIS WAVE CONTINUES TO BE A CHALLENGE TO TRACK AS
THERE IS NO WELL-DEFINED...LOW-LEVEL CLOUD SIGNATURE EVIDENT IN
VISIBLE SATELLITE IMAGERY. ITS CURRENT POSITION IS BASED
PRIMARILY
ON EXTRAPOLATION AND WEAK CYCLONIC SHEAR S OF 15N. WIDELY
SCATTERED MODERATE CONVECTION IS OVER THE W CARIBBEAN SEA FROM
12N-19N BETWEEN 76W-85W. SOME OF THIS CONVECTION COULD BE
ASSOCIATED WITH THE WAVE...ENHANCED BY THE END OF A MID- TO
UPPER-LEVEL TROUGH EXTENDING SW INTO THE NW CARIBBEAN.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 07N12W TO 03N26W TO 2S31W TO 05N38W.
LARGE CLUSTERS OF SCATTERED MODERATE TO STRONG CONVECTION ARE
MOVING OFF THE W AFRICAN COAST FROM 4N-14N BETWEEN 11W-18W.
OTHER CLUSTERS OF MODERATE TO STRONG CONVECTION ARE OCCURRING
WITHIN 360 NM EITHER SIDE OF AXIS BETWEEN 23W AND 36W. ELSEWHERE
...SCATTERED MODERATE ISOLATED CONVECTION IS OCCURRING BETWEEN
02S AND 06S BETWEEN 16W AND 22W.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY...UPPER-AIR DATA...AND CLOUD-TRACKED WINDS
INDICATE AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDS FROM THE
FL PENINSULA WESTWARD THROUGH NE MEXICO. STRONG LARGE-SCALE
SINKING ASSOCIATED WITH THE RIDGE IS CARVING OUT A LARGE AREA
VOID OF ANY ORGANIZED CONVECTION...NOT TO MENTION ANY
SIGNIFICANT CLOUD COVER. IT SHOULD BE NOTED THAT THE LACK OF
DEEP CONVECTION OVER THE GULF REGION CERTAINLY IS A BIT
ANOMALOUS FOR THIS TIME OF YEAR. LOW-LEVEL SUBTROPICAL RIDGING
BULGES WSW INTO THE GULF AND IS PROVIDING A GENERAL SE TO S 10
TO 15 KT FLOW OVER THE EASTERN HALF OF THE GULF...WHILE A
STRONGER 15 TO 20 KT FLOW PREVAILS W OF 90W. THE ONLY DENSE
CLOUD COVER OF NOTE IS OVER THE BAY OF CAMPECHE...WHERE VISIBLE
SATELLITE IMAGERY SHOWS THE REMNANTS OF TROPICAL STORM ARTHUR
TRUDGING SLOWLY WNW JUST SE OF VERA CRUZ. ALTHOUGH A FAIR
AMOUNT OF CONVECTION HAD DEVELOPED IN ASSOCIATION WITH EX-ARTHUR
OVERNIGHT...LITTLE REMAINS EARLY THIS AFTERNOON EXCEPT FOR A FEW
CONVECTIVE ELEMENTS BLOWING SE BETWEEN VILLAHERMOSA AND
CAMPECHE. WITH THE CENTER VERY NEAR THE COAST AND MOVING INLAND
AND THE LATEST CIMMS ANALYSIS SHOWS UP TO 15 KT OF NW SHEAR
...THE CHANCE FOR RE-DEVELOPMENT SEEMS SLIM.

OVER THE NEXT FEW DAYS...EXPECT THE STRONG MID- TO UPPER-LEVEL
RIDGE TO SHIFT E/NE AS A DEEP SHORTWAVE TROUGH PUSHES OUT OF THE
WESTERN STATES AND ONTO THE PLAINS. AS A RESULT...DEEP LOW
PRESSURE SHOULD FORM OVER THE PLAINS AND LEAD TO A BRISK RETURN
FLOW AND INCREASING SEAS ACROSS MUCH OF THE GULF DURING THE NEXT
36 TO 48 HOURS. ALTHOUGH WEAK...THE REMAINS OF ARTHUR SHOULD
MOVE INLAND NW OF VERA CRUZ AND POSSIBLY ENHANCE RAINS OVER THE
SIERRA MADRE ORIENTAL S OF TUXPAN. OTHERWISE...UNUSUALLY DRY
CONDITIONS ARE EXPECTED OVER THE GULF THROUGH AT LEAST LATE
WEEK.

CARIBBEAN...
WATER VAPOR AND CLOUD-TRACKED WINDS SHOW THE WESTERN END OF WEAK
MID- TO UPPER-LEVEL RIDGING EXTENDING INTO THE EASTERN CARIBBEAN
TO ABOUT 70W. TO THE W...A WELL-DEFINED MID- TO UPPER-LEVEL
TROUGH INTERRUPTS THE CARIBBEAN RIDGING...WITH AN AXIS FROM THE
WINDWARD PASSAGE TO AROUND 13N80W. AS MENTIONED...TWO TROPICAL
WAVES ARE MARCHING WESTWARD UNDERNEATH THESE FEATURES...SEE
ABOVE. THE SECOND WAVE...NOW ALONG 65/66W...HAS BEGUN TO
INTERACT WITH THE MID- TO UPPER-LEVEL TROUGH HANGING INTO THE N
CENTRAL CARIBBEAN...WHICH HAS RESULTED IN ENHANCED CLOUD COVER
AND CONVECTION EXTENDING FROM JAMAICA AND HISPANIOLA NE INTO THE
SW ATLC WATERS. WITH THE UPPER TROUGH LIKELY TO REMAIN NEARLY
STATIONARY THE NEXT DAY OR TWO...THE FAVORABLE DIVERGENT FLOW
ALOFT...ENHANCED INSTABILITY...AND THE TRANSIENT WAVE MOVING
THROUGH THE REGION SHOULD LEAD TO SCATTERED TO LOCALLY NUMEROUS
TSTMS E OF THE AXIS. SCATTERED CONVECTION IS ALSO FIRING ALONG
THE NORTHERN END OF THE TROPICAL WAVE NOW ALONG 81W...POSSIBLY
BECAUSE OF ITS INTERACTION WITH THE SAME UPPER-LEVEL TROUGH.
ENHANCED CLOUD COVER AND SOME CONVECTION ALSO CONTINUE TO PLAGUE
PARTS OF THE YUCATAN...BELIZE...AND GUATEMALA...IN A REGION
WHERE THE ELY TRADES ARE MEETING A PERSISTENT MONSOONAL FLOW
STILL DOMINATING THE TROPICAL EASTERN PACIFIC W OF 100W.
OTHERWISE...NEAR NORMAL SURFACE RIDGING AND LIGHT TO MODERATE
TRADES PREVAIL ACROSS THE CARIBBEAN BASIN.

ATLANTIC...
ENHANCED MID-LEVEL RIDGING EXTENDS FROM NW AFRICA TO N OF THE
LESSER ANTILLES...WITH A PRONOUNCED BREAK NOTED W OF THERE
BETWEEN 60-75W. WATER VAPOR IMAGERY REVEALS A TROUGH ACROSS
THIS REGION EXTENDING FROM JUST W OF BERMUDA SSW TO THE WINDWARD
PASSAGE. A FAVORABLE DIFFLUENT FLOW ALOFT...ENHANCED LOW-LEVEL
MOISTURE ASSOCIATED WITH THE NORTHERN END OF A TROPICAL WAVE
OVER THE EASTERN CARIBBEAN...AND ENHANCED INSTABILITY ARE
RESULTING IN A LARGE AREA OF CLOUD COVER AS WELL AS A SOLID AREA
OF CONVECTION FROM 20-23N BETWEEN 65W TO THE SERN BAHAMAS.
MODELS SHOW THE TROUGH EDGING EASTWARD DURING THE NEXT 12 TO 24
HOURS AND ULTIMATELY LIFTING OUT BUT NOT BEFORE DEPOSITING A
CYCLONIC CIRCULATION NEAR 25N64W BY FRI MORNING. INDICATIONS
ARE THAT THIS FEATURE AS WELL AS ANOTHER SIMILAR ONE TO THE W
WILL GET CAUGHT IN AN ENHANCED EASTERLY CURRENT TO THE S OF
ENHANCED MID-LEVEL RIDGING OVER THE SW ATLC/SERN STATES LATER
THIS WEEK. THIS COULD END UP PROVIDING PORTIONS OF THE BAHAMAS
AND FL WITH SOME MUCH-NEED RAINFALL BY THE WEEKEND.

ELSEWHERE...THE LATEST CIMSS SAHARAN AIR LAYER ANALYSIS REVEALS
A LARGE AREA OF DUST AND STRONG SUBSIDENCE ASSOCIATED WITH THE
TROPICAL WAVE ALONG 40W...FOLLOWED BY A SECOND AREA NOW EMERGING
FROM NW AFRICA AHEAD OF THE NEXT WAVE. THE WAVE ALONG 40W
APPEARS TO BE OF HIGH AMPLITUDE FOR THIS TIME OF YEAR...WITH AN
EXTENSION AT LEAST TO 20N. CIMSS SHEAR ANALYSES AS WELL AS CIRA
EXPERIMENTAL GENESIS PRODUCTS SHOW MUCH LOWER-THAN-AVERAGE
VERTICAL WIND SHEAR S OF ABOUT 18N E OF 55W...A TREND WHICH HAS
CONTINUED FOR SOME TIME. HOWEVER...EVEN THOUGH SEA SURFACE
TEMPERATURES ARE ABOVE CLIMATOLOGICAL AVERAGES...THEY ARE STILL
TOO COOL OVER MUCH OF THE TROPICAL ATLANTIC FOR TROPICAL CYCLONE
DEVELOPMENT.

$$
KIMBERLAIN


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