[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 251042
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SAT AUG 25 2007

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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1015 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 24W/25W S OF 20N MOVING W 10-15 KT. AFTER
MOVING SLUGGISHLY WWD OVER THE PAST DAY OR SO IT LOOKS LIKE THE
SYSTEM HAS PICKED UP SPEED...WHICH MAKES SENSE GIVEN THE
INCREASED 600-850 MB ELY JET INIDCATED IN THE NEARBY SOUNDINGS.
EARLY VIS IMAGES SHOW BROAD TURNING IN THE STRATOCUMULUS CLOUDS
SUGGESTING THE AXIS COULD BE CLOSER TO 26W. A 7Z QSCAT PASS AND
DATA FROM THE CAPE VERDE ISLANDS INDICATE LITTLE ASSOCIATION AT
THE SFC BUT...THE LOW TO MID LEVEL CLOUD DRIFT WINDS SHOW THE
BROAD GYRE STRUCTURE MENTIONED ABOVE. SCATTERED SHOWERS AND
TSTMS ARE LINEAR IN SHAPE EMBEDDED IN THE ITCZ FROM 11N-13N E OF
25W.

TROPICAL WAVE IS ALONG 50W S OF 14N MOVING W 10 KT. THIS SYSTEM
APPEARS TO HAVE BECOME A LITTLE BETTER ORGANIZED WITH LOW LEVEL
TURNING CLEARLY APPARENT ON VIS IMAGES...THOUGH STILL WELL
EMBEDDED IN THE ITCZ. SCATTERED SHOWERS AND TSTMS ARE CONFINED
TO THE INTERSECTION OF THE ITCZ FROM 8N-11N WITHIN 180 NM EITHER
SIDE OF THE WAVE AXIS. A SIDE NOTE...IT'S DIFFICULT TO
DECIPHER IF THIS IS A TROPICAL WAVE (ORIGINATING FROM AFRICA) OR
A DISTURBANCE WITHIN THE ITCZ. A HIGHER AMPLITUDE WAVE LIKE
FEATURE APPEARS TO BE APPROACHING THE LESSER ANTILLES. FOR NOW
ANALYZED THE NRN PART OF THAT FEATURE AS A TROUGH BUT DAY SHIFT
MAY MAKE SOME ADJUSTMENTS.

TROPICAL WAVE IS IN THE W CARIBBEAN ALONG 81W S OF 18N MOVING W
15-20 KT OVER THE PAST 24 HRS. IR IMAGES SHOWS A BIT OF
CURVATURE TO THE SHOWER/TSTM ACTIVITY NEAR THE BASE OF THE WAVE
EMBEDDED WITHIN THE ITCZ S OF 11N BETWEEN 77W-83W.
OTHERWISE...LITTLE SIGNATURE OR SHOWER ACTIVITY IS APPARENT IN
THE AVAILABLE DATA ACROSS THE REMAINDER OF THE AXIS.

THE NRN PORTION OF A HIGH AMPLITUDE TROPICAL WAVE EXTENDS INTO
THE S GULF ALONG 89W S OF 24N MOVING W 10-15 KT. LOW-LEVEL LIFT
ASSOCIATED WITH THIS WAVE AND DIFFLUENCE ALOFT IS GENERATING
SCATTERED TSTM ACTIVITY OVER S MEXICO AND THE BAY OF CAMPECHE.
AN AREA OF LOW PRES HAS FORMED NEAR THE SRN EXTENSION OF THE
WAVE IN THE GULF OF TEHUANTEPEC...SEE THE EPAC TWD FOR DETAILS.
EARLIER SHIP/BUOY DATA DID INDICATE SOME SFC TURNING AND
SLIGHTLY LOWER PRESSURES NEAR THIS WAVE IN THE GULF...ALTHOUGH
THE SIGNAL HAS DAMPENED OVER THE PAST SEVERAL HOURS.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N16W 8N26W 10N47W 10N64W. BESIDES
FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...
SCATTERED SHOWERS AND TSTMS ARE WITHIN 60 NM S OF THE AXIS
BETWEEN 25W-36W.

DISCUSSION...

GULF OF MEXICO...
A WELL DEFINED UPPER LOW IS CENTERED ACROSS THE MID GULF NEAR
27N89W. INSTABILITY ASSOCIATED WITH THIS UPPER CIRCULATION AND
S-SWLY FLOW ALOFT E OF THE CENTER IS ADVECTING MOISTURE ACROSS
THE ERN HALF OF THE GULF AND FLORIDA. MOST OF THE ASSOCIATED
TSTM ACTIVITY FROM EARLIER HAS DIMINISHED THOUGH LEFTOVER
ISOLATED SHOWERS/TSTMS ARE IN THE S CENTRAL GULF LIKELY ENHANCED
SOME BY A TROPICAL WAVE IN THE REGION. CONVECTION REMAINS FIRED
UP OVER SRN MEXICO AND IN THE BAY OF CAMPECHE. DIFFLUENCE ALOFT
APPEARS TO BE THE PRIMARY TRIGGER THOUGH NO DOUBT THERE IS
INFLUENCE FROM THE NEARBY TROPICAL WAVE AND SMALLER SCALE FLOWS.
THE SFC PATTERN IS VERY TRANQUIL WITH WEAK RIDGING FROM THE ATLC
STRETCHING JUST N OF THE AREA. THIS IS KEEPING E TO SELY SFC
FLOW ON THE LIGHT SIDE. LITTLE CHANGE IN THE SFC PATTERN IS
EXPECTED OVER THE NEXT COUPLE OF DAYS SO WINDS ARE ANTICIPATED
TO REMAIN LIGHT.

CARIBBEAN SEA...
MOST OF THE CARIB IS FAIRLY QUIET THIS MORNING THOUGH THERE ARE
A FEW AREAS EXPERIENCING SOME UNSETTLED WEATHER. THE MOST ACTIVE
IS IN THE SW CARIB WHERE A TROPICAL WAVE IS ENHANING ITCZ
RELATED CONVECTION...SEE ABOVE FOR DETAILS. ELSEWHERE MUCH OF
THE SENSIBLE WEATHER/MOISTURE APPEARS RELATED TO FEATURES ALOFT.
THE MID AND UPPER PATTERN CONSISTS OF A N-S STRETCHED HIGH PRES
RIDGE CENTERED OVER CENTRAL CUBA AND AN ELONGATED TROUGH
EXTENDING FROM THE ATLC ACROSS THE NRN LEEWARDS TOWARD THE COAST
OF COLOMBIA. STRONG N TO NELY FLOW BETWEEN THESE FEATURES HAS
BLOWN OFF LAST EVENING'S TSTM ACTIVITY OVER E CUBA AND
HISPANIOLA INTO THE COASTAL WATERS TO NEAR JAMAICA. NEARLY ALL
OF THE SHOWERS ARE DIMINISHING EXCEPT FOR ONE CLUSTER TO THE S
OF HAITI WHICH ACTUALLY LOOKS LIKE IT'S EXPANDING. MUCH OF THE
REMAINDER OF THE CENTRAL CARIB LIES IN AN UPPER CONFLUENT ZONE
HELPING TO SINK AND SUPPRESS DEEP CLOUD COVER. HIGH LEVEL
CLOUDINESS LIES OVER THE E CARIB ON THE E SIDE OF THE TROUGH AND
OVER THE W CARIB EMBEDDED WITHIN THE RIDGE.

ATLANTIC OCEAN...
THE SFC PATTERN ACROSS THE ATLC DISCUSSION AREA REMAINS WEAK
THIS MORNING. THIS WEAK PATTERN IS MAINLY DUE TO AN UNUSUAL (FOR
AUGUST) COLD FRONT DEEP INTO THE SUBTROPICS ENTERING THE AREA
NEAR 32N42W TO A 1012 MB LOW NEAR 28N52W CONTINUING ALONG 25N60W
THEN DISSIPATING TO 31N67W. A RECENT QSCAT PASS DEPICTED THIS
BOUNDARY WELL...MARKING IT AS A PRONOUNCED NLY WIND SHIFT AND
INCREASE TO 20 KT ON THE N SIDE NEAR THE LOW. SATELLITE IMAGERY
ALSO SHOWS SCATTERED SHOWERS WITHIN 60 NM AHEAD OF THE BOUNDARY
AND A SCATTERED STABLE STRATOCUMULUS DECK BEHIND IT. A WEAK
LOW-LEVEL TROUGH IS ANALYZED ALONG 55W FROM 15N-21N. THIS
BOUNDARY IS NOT PRODUCING ANY SIGNIFICANT SHOWER ACTIVITY BUT
DOES SHOW UP WELL IN CLOUD DRIFT WINDS AND ON SATELLITE IMAGERY.
THESE LOW-LATITUDE BOUNDARIES HAVE GREATLY BROKEN UP THE TYPICAL
SUBTROPICAL RIDGING ALLOWING TRADES TO BE FAIRLY LIGHT ACROSS
THE BULK OF THE AREA.

IN THE MID AND UPPER LEVELS...A RIDGE IS OVER THE W ATLC
CENTERED VERY NEAR BERMUDA. A DIFFLUENT PATTERN LIES AT THE
W EDGE OF THE RIDGE ASSOCIATED WITH SOME TROUGHING OVER THE
BAHAMAS AND IN THE GULF OF MEX. THIS DIFFLUENCE IS PRODUCING A
FAIR AMOUNT OF CLOUDINESS ACROSS THE AREA W OF 76W. A LARGER
SCALE TROUGH...THE SUPPORT FOR THE FRONT DISCUSSED ABOVE...IS
OVER THE CENTRAL ATLC EXTENDING FROM 32N45W TO AN UPPER LOW NEAR
22N57W CONTINUING INTO THE E CARIB. A DOMINATING WELL DEFINED
RIDGE TAKES OVER IN THE E ATLC WITH THE MAIN ANTICYCLONE
CENTERED NEAR 20N37W. OUTSIDE OF THE AREAS OUTLINED IN THE ABOVE
PARAGRAPH...DRY AIR ALOFT IS WIDESPREAD ON WATER VAPOR IMAGERY.

$$
CANGIALOSI


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