Thursday Afternoon Tropical Weather Discussion

AXNT20 KNHC 051819
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU JUN 05 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...

TROPICAL WAVE IS INTRODUCED ALONG 23W S OF 16N MOVING W 15 KT.
SOUNDING DATA FROM DAKAR STILL REVEALS A STRONG RISE/FALL
COUPLET IN SEVERAL DIFFERENT FIELDS...WITH THE MOST NOTABLE
BEING 2-3 MB PRESSURE RISES TODAY IN THE WAKE OF THIS FEATURE.
MIMIC-TPW ANIMATION ALSO SHOWS A NEW SURGE OF DEEP MOISTURE
RISING TO 15N ALONG 20W IN ASSOCIATION WITH THIS WAVE....AND THE
LATEST SFC ANALYSIS SHOWS A NORTHWARD RISE IN THE ITCZ. ALTHOUGH
RECENT METEOSAT IMAGERY IS UNAVAILABLE...MORNING IMAGES DID
INDICATE SCATTERED TO WIDESPREAD CONVECTION FROM 04N TO 09N
BETWEEN 21W AND 28W...IN AN UNUSUAL LOCATION W OF THE AXIS.

TROPICAL WAVE IS ALONG 49W S OF 21N IS MOVING W 15 KT. DEEP
CONVECTION IS ENTIRELY ABSENT...AS THE WAVE IS MOVING OVER
SUB-26.5C SEA SURFACE TEMPERATURES OVER THE TROPICAL ATLANTIC.
COINCIDING WITH THE LOSS OF ALL DEEP CONVECTION...THE WAVE HAS
BECOME HARDER TO DISCERN USING MIMIC-TPW ANIMATION. IN FACT... A
BROAD CYCLONIC ENVELOPE WAS NOTED YESTERDAY IN MIMIC-TPW IMAGERY
...WHICH IS IN SHARP CONTRAST TO TODAYS MORNING DISORGANIZED
APPEARANCE. IN ADDITION...A WEAK CYCLONIC CIRCULATION STILL
EXISTS AT THE BASE OF THE WAVE...THOUGH IT TOO IS LOSING ITS
ORGANIZATION.

TROPICAL WAVE IS IN THE W CENTRAL CARIBBEAN ALONG 75W S OF 16N
MOVING W 10-15 KT. LITTLE TO NO DEEP CONVECTION IS ASSOCIATED
WITH THIS FEATURE ANY LONGER...AND THERE IS NO HINT OF A
CYCLONIC CURVATURE TO THE LOW-LEVEL WIND. HOWEVER...TIME SERIES
DATA FROM CURACAO DOES INDICATE A MAXIMUM IN THE 850 MB WINDS
TODAY...POSSIBLY A SIGN OF THE WAVES EXISTENCE. OTHER SOUNDING
DATA FROM THE CARIBBEAN DOES NOT APPEAR USEFUL...AS THE WAVE
REMAINS OF FAIRLY LOW AMPLITUDE. GIVEN THE DIFFICULTY IN
ESTABLISHING THE WAVES POSITION...THE WAVE IS LARGELY BEING
EXTRAPOLATED WESTWARD.

TROPICAL WAVE IN THE W CARIBBEAN ALONG 87/88W HAS BECOME
DIFFICULT TO FIND USING CONVENTIONAL DATA. THIS CASE IS NOT
ISOLATED...AS SEVERAL OF THE MOST RECENT WAVES MOVING ACROSS
THIS REGION HAVE PROPAGATED INTO THE HIGHLY ANOMALOUS
ENVIRONMENT WHICH HAS PREVAILED IN THE VICINITY OF CENTRAL
AMERICA AND THE TROPICAL EAST PACIFIC S OF MEXICO SINCE LATE
MAY. THE ANOMALOUS ENVIRONMENT IS CHARACTERIZED BY A LACK OF
EASTERLY TRADES BLOWING ACROSS CENTRAL AMERICA AND THE TROPICAL
EAST PACIFIC E OF 100W...WITH AN UNUSUAL LOW-LEVEL WLY FLOW IN
PLACE INSTEAD. AS THE WAVE HAS BECOME ASSIMILATED INTO THIS
MONSOON-TYPE ENVIRONMENT..IT IS NOW CARRIED AS A TROUGH AND IS
EXTRAPOLATED FORWARD.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 12N16W TO 03N27W TO 00N35W TO
01S47W. METEOSAT IMAGERY IS UNAVAILABLE AT THIS HOUR TO DESCRIBE
CURRENT CONVECTION.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY AND UPPER-AIR DATA INDICATE AN AMPLIFIED
MID- TO UPPER-LEVEL RIDGE SITS OVER THE EASTERN THIRD OF THE
COUNTRY...WITH THE RIDGE CENTER JUST N OF THE FL PANHANDLE.
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 FOR SEVERAL
DAYS IN A ROW NOW CERTAINLY IS A BIT ANOMALOUS FOR THIS TIME OF
YEAR. LOW-LEVEL SUBTROPICAL RIDGING BULGES WSW FROM THE ATLANTIC
INTO THE GULF AND IS PROVIDING A GENERAL SE 10 TO 15 KT FLOW
OVER THE EASTERN HALF OF THE GULF...WHILE A SE TO S 20 TO 25 KT
FLOW PREVAILS W OF 90W. THE ONLY CLOUD COVER OF NOTE IS OVER THE
BAY OF CAMPECHE IN ASSOCIATION WITH A WEAK MID-LEVEL CYCLONIC
CIRCULATION NOTED NEAR 19N97W. ISOLATED CONVECTION POSSIBLY
RELATED TO THIS FEATURE IS BEGINNING TO DEVELOP ALONG THE W
COAST OF THE YUCATAN PENINSULA.

A STRONG CUT-OFF CYCLONE EMBEDDED WITHIN AN UNUSUALLY DEEP AND
BROAD TROUGH OF LOW PRESSURE OVER THE WESTERN HALF OF THE
COUNTRY WILL BE FORCED NE INTO THE NORTHERN PLAINS AND UPPER
MIDWEST TODAY THROUGH FRI...BLOCKED BY THE AMPLIFIED RIDGE NOW
OVER THE EASTERN STATES. AS A RESULT...A STRENGTHENED PRESSURE
GRADIENT BETWEEN DEEP SFC LOW PRESSURE OVER THE PLAINS AND
RELATIVE HIGH PRESSURE TO THE EAST SHOULD LEAD TO STRONG RETURN
FLOW OF UP TO 30 KT AND SEAS BUILDING UP TO 8 TO 11 FT OVER THE
NW GULF WATERS. WINDS SHOULD DECREASE TO 15 TO 20 KT ACROSS THE
GULF BY FRI AFTERNOON...WITH LITTLE CHANGE TO CURRENT PATTERN
GOING INTO THE WEEKEND.

CARIBBEAN...
WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS SHOW THE WESTERN END
OF A WEAK MID- TO UPPER-LEVEL RIDGE EXTENDING INTO THE EASTERN
CARIBBEAN TO ABOUT 73W. TO THE W...A WEAKENING MID- TO UPPER-
LEVEL TROUGH INTERRUPTS THE CARIBBEAN RIDGING...WITH AN AXIS
EXTENDING FROM THE WINDWARD PASSAGE TO AROUND 15N80W. EVEN
THOUGH THE UPPER TROUGH IS GRADUALLY WEAKENING...THE FAVORABLE
DIVERGENT FLOW ALOFT...ENHANCED INSTABILITY...AND THE PRESENCE
OF A TRANSIENT WAVE NOW ALONG 75W MOVING THROUGH THE REGION
SHOULD LEAD TO SCATTERED CONVECTION ACROSS JAMAICA AND
HISPANIOLA TODAY. HOWEVER...IT APPEARS AS IF THE MAIN FOCUS OF
THE CONVECTION WILL REMAIN N OF HISPANIOLA THIS AFTERNOON AND
THIS EVENING...SIMILAR TO YESTERDAY. SCATTERED CONVECTION IS
ALSO BEGINNING TO BREAK OUT OVER COASTAL SECTIONS FROM COSTA
RICA THROUGH NE HONDURAS...VERY CLOSE TO THE REGION WHERE THE
ELY TRADES ARE MEETING THE WEAK MONSOON-TYPE WESTERLY FLOW FROM
THE TROPICAL EAST PACIFIC. IN ADDITION...ENHANCED CLOUD COVER
AND SCATTERED CONVECTION CONTINUES TO PLAGUE PARTS OF THE
YUCATAN ...BELIZE...AND GUATEMALA...NEAR WHERE THE LATEST
TROPICAL WAVE IN A SERIES HAS BECOME ASSIMILATED INTO A
LARGER-SCALE MONSOON GYRE NEAR OR JUST S OF THE ISTHMUS OF
TEHUANTEPEC.

OVER THE NEXT FEW DAYS...THE NARROW MID- TO UPPER-LEVEL TROUGH
OVER THE N CENTRAL CARIBBEAN SHOULD DISSIPATE...THOUGH THE
TROUGH WILL LEAVE BEHIND AN UPPER TROPOSPHERIC COLD LOW N OF
HISPANIOLA. ITS PRESENCE SHOULD CONTINUE TO ENHANCE THE
POTENTIAL FOR CONVECTION OVER THE N CENTRAL CARIBBEAN.
OTHERWISE...UNDER CLIMATOLOGICALLY AVERAGE TO SLIGHTLY BELOW
AVERAGE SUBTROPICAL RIDGING...MODERATELY STRONG TRADES SHOULD
PREVAIL E OF 75W...WHILE LIGHT TO MODERATE TRADES PREVAIL
ELSEWHERE.

ATLANTIC...
ENHANCED MID-LEVEL RIDGING GENERALLY EXTENDS FROM 40W TO NE OF
THE LESSER ANTILLES...WITH A PRONOUNCED BREAK IN SUBTROPICAL
RIDGING W OF THERE FROM 55-75W. WITHIN THIS BREAK...WATER VAPOR
IMAGERY INDICATES A VIGOROUS MID- TO UPPER-LEVEL COLD LOW NEAR
25N66W MOVING LITTLE. HOWEVER...THE LARGER-SCALE TROUGH IN WHICH
ITS EMBEDDED APPEARS TO BE EDGING EAST. A FAVORABLE DIFFLUENT
FLOW ALOFT E OF THE TROUGH AXIS...ENHANCED MOISTURE AT ALL
LEVELS ...AND ENHANCED INSTABILITY ARE RESULTING IN A LARGE AREA
OF CLOUD COVER AS WELL AS A GROWING AREA OF CONVECTION WITHIN
120 NM EITHER SIDE OF A LINE FROM 20N69W TO 25N62W. SPORADIC
CONVECTION IN THE VICINITY OF THE COLD LOW AND E OF THE UPPER
TROUGH SHOULD PERSIST THROUGH FRI...WITH MODELS SHOWING THE COLD
LOW HEADING W BY THE WEEKEND IN AN ELY CURRENT ALOFT. IN THE
END...THIS SHOULD RESULT IN A GRADUAL INCREASE IN RAIN CHANCES
OVER THE BAHAMAS AND EVENTUALLY THE FL PENINSULA SAT THROUGH
MON.

ELSEWHERE...THE LATEST CIMSS SAHARAN AIR LAYER ANALYSIS REVEALS
A LARGE AREA OF DUST AND STRONG SUBSIDENCE ASSOCIATED WITH THE
WAVE JUST NOW EMERGING FROM NW AFRICA AND SPREADING AS FAR E AS
40W. THE PRESENCE OF THE SAL SURROUNDING THE NEWEST WAVE TO MOVE
OFFSHORE IS LIKELY INHIBITING CONVECTION OVER THE AREA N OF 11N.
OTHERWISE...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
SINCE AT LEAST MAY. IN FACT...THE AREA AVERAGE SHEAR ACROSS THE
TROPICAL ATLANTIC IS LESS THAN 20 KT...WHEN IT SHOULD BE MUCH
CLOSER TO 30 KT. DESPITE THE EARLIER-THAN-NORMAL DYNAMIC
POTENTIAL OVER THE TROPICAL ATLANTIC...ABOVE NORMAL SEA SURFACE
TEMPERATURES ARE STILL TOO COOL OVER MUCH OF THE TROPICAL
ATLANTIC FOR TROPICAL CYCLONE DEVELOPMENT.

$$
KIMBERLAIN


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