[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 121759
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED SEP 12 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...SPECIAL FEATURES...

SEPTEMBER IS CLIMATOLOGICALLY THE MOST ACTIVE MONTH OF THE
TROPICAL SEASON IN THE ATLANTIC BASIN. THIS MORNING...TWO
TROPICAL DEPRESSIONS HAVE FORMED. ONE IN THE NORTHWESTERN GULF
OF MEXICO AND THE OTHER ONE WELL EAST OF THE LESSER ANTILLES. AT
12/1800 UTC TROPICAL DEPRESSION NINE IS UPGRADED TO TROPICAL
STORM HUMBERTO...THE EIGHTH NAMED STORM OF THE 2007 ATLANTIC
HURRICANE SEASON.

THE AREA OF LOW PRESSURE LOCATED EAST OF THE LESSER ANTILLES HAS
ACQUIRED ENOUGH ORGANIZATION TO BE DECLARED A TROPICAL
DEPRESSION...THE EIGHTH OF THE ATLANTIC SEASON. AT 12/1500 UTC
THIS SYSTEM WAS CENTERED NEAR 13.2N 44.6W...OR ABOUT 980 NM EAST
OF THE LESSER ANTILLES. IT IS MOVING WEST-NORTHWEST AT 10 KT.
MAXIMUM SUSTAINED WINDS SPEED IS 30 KT WITH GUSTS TO 40 KT.
SOME STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS AND THE
DEPRESSION COULD BECOME A TROPICAL STORM LATER TODAY OR TONIGHT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB. SEE LATEST
NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23
KNHC FOR MORE DETAILS. NUMEROUS MODERATE TO ISOLATED STRONG
CONVECTION IS JUST WEST OF THE CENTER FROM 12N-14N BETWEEN
44W-46W.

RADAR...SATELLITE...AND BUOY OBSERVATIONS INDICATE THAT THE AREA
OF LOW PRESSURE IN THE WESTERN GULF OF MEXICO HAS BECOME BETTER
ORGANIZED THIS MORNING. LATEST DOPPLER RADAR OBSERVATIONS SHOW
THAT THIS SYSTEM IS GETTING BETTER ORGANIZED...WITH MORE BANDING
FEATURES.  AT 12/1500 THIS SYSTEM WAS UPGRADED TO A TROPICAL
DEPRESSION STATUS. THREE HOURS LATER...IT WAS CLASSIFIED AS A
TROPICAL STORM HUMBERTO. AT 12/1800 HUMBERTO WAS CENTERED NEAR
28.3N 95.1W...OR ABOUT 60 NM SOUTH-SOUTHWEST OF GALVESTON TEXAS
AND ABOUT 125 NM EAST-NORTHEAST OF CORPUS CHRISTI TEXAS. IT IS
MOVING TOWARD THE NORTH AT 5 KT. MAXIMUM SUSTAINED WINDS SPEED
IS 40 KT WITH HIGHER GUSTS. ESTIMATED MINIMUM CENTRAL PRESSURE
IS 1005 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO
HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. BANDS OF SHOWERS
WITH EMBEDDED TSTMS ASSOCIATED WITH THIS TROPICAL CYCLONE ARE
ALREADY AFFECTING PARTS OF THE UPPER TEXAS COAST AND SW
LOUISIANA. RAINFALL AMOUNTS OF 5 TO 10 INCHES ARE EXPECTED ALONG
THE MIDDLE AND UPPER TEXAS COAST AND IN EXTREME SOUTHWESTERN
LOUISIANA...WITH ISOLATED MAXIMUM ACCUMULATIONS OF 15 INCHES
POSSIBLE.

...TROPICAL WAVES...

A HIGH AMPLITUDE TROPICAL WAVE IS IN THE E ATLC ALONG 34W/35W S
OF 24N MOVING W 15 KT. IN GENERAL...THIS WAVE HAS CHANGED LITTLE
OVER THE PAST COUPLE OF DAYS. THE STRUCTURE REMAINS WELL DEFINED
WITH A LARGE SHIELD OF CYCLONIC TURNING NOTED IN THE LOW TO MID
LEVEL CLOUD FIELD. IN ADDITION...THE UW-CIMSS TPW ANIMATION
REVEALS A LARGE WWD PROPAGATING SURGE OF MOISTENED AIR. DESPITE
THE FAIR STRUCTURE...DEEP MOISTURE IS MINIMAL WITH WIDELY
SCATTERED SHOWERS AND TSTMS FROM 17N-20N BETWEEN 31W-36W.

TROPICAL WAVE IS IN THE CENTRAL CARIB ALONG 73W S OF 21N MOVING
W 15-20 KT. A SURGE OF MOISTURE ASSOCIATED WITH THIS FEATURE IS
WELL DEFINED ON THE TROPICAL PRECIPITABLE WATER ANIMATION FROM
CIMSS. THE WAVE IS INTERACTING WITH AN UPPER LOW CURRENTLY
LOCATED OVER E CUBA. THE WAVE IS HELPING TO INDUCE SOME SHOWER
ACTIVITY OVER HISPANIOLA AND WESTERN VENEZUELA.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N15W 14N32W 13N40W 10N47W 8N63W.
WIDELY SCATTERED MODERATE CONVECTION IS 6N-14N EAST OF 25W...
AND FROM 5N-11N BETWEEN 28W-35W. SCATTERED MODERATE TO ISOLATED
STRONG CONVECTION IS OVER NE VENEZUELA AND NW GUYANA. SIMILAR
CONVECTION IS ALSO SEEN APPROACHING THE WEST AFRICAN COAST
LIKELY ASSOCIATED WITH THE NEXT TROPICAL WAVE. THE VERTICAL
SOUNDING FROM DAKAR SHOWS THAT THE WAVE IS JUST THERE.

DISCUSSION...

THE GULF OF MEXICO...
THE BIG WEATHER STORY OF THE DAY IS THE DEVELOPMENT OF TROPICAL
DEPRESSION NINE OVER THE NW PORTION OF THE GULF. SEE SPECIAL
FEATURES FOR MORE DETAILS. WATER VAPOR IMAGES AND THE CIMSS TPW
PRODUCT SHOW A MOISTENED ATMOSPHERE ACROSS THE ENTIRE AREA. AN
UPPER RIDGE ANCHORED ON A HIGH OVER CENTRAL MEXICO COVERS THE
WESTERN HALF OF THE GULF AND THE N GULF WATERS WHILE THE BROAD
CYCLONIC CIRCULATION OF AN UPPER LOW LOCATED OVER E CUBA
DOMINATES THE REMAINDER OF THE GULF WITH N AND NE UPPER LEVEL
FLOW. A STATIONARY FRONTAL BOUNDARY IS ANALYZED JUST INLAND
ACROSS THE GULF COAST STATES. THIS BOUNDARY IS NOT EXPECTED TO
PUSH VERY FAR...IF AT ALL...INTO THE OFFSHORE WATERS TODAY
BEFORE RETREATING AND WEAKENING. A WEAK SURFACE TROUGH RUNS FROM
27N84W TO 23N85W. MOSAIC DOPPLER RADAR FROM THE SE US...SHOWS
SCATTERED SHOWERS AND ISOLATED TSTMS OVER THE EASTERN GULF...
EAST OF 86W RELATED TO THE THIS TROUGH.

THE CARIBBEAN SEA...
THE BROAD CYCLONIC CIRCULATION ASSOCIATED WITH AN UPPER LOW
CURRENTLY SPINNING OVER ERN CUBA COVERS MOST OF THE WEST AND
CENTRAL CARIBBEAN WHILE AN UPPER HIGH IN THE TROPICAL ATLC
DOMINATES THE EASTERN CARIBBEAN AND THE LESSER ANTILLES. THE
EPAC ITCZ COUPLED WITH A DIFFLUENT PATTERN ALOFT IS ENHANCING
CLUSTERS OF SCATTERED MODERATE TO ISOLATED STRONG CONVECTION
OVER THE SW CARIBBEAN...INCLUDING ALSO PARTS OF PANAMA...COSTA
RICA AND NICARAGUA. A TROPICAL WAVE APEX EXTENDS FROM HAITI TO
COLOMBIA. SEE ABOVE. MODERATE TO STRONG TRADE WINDS ARE BLOWING
ACROSS THE CARIBBEAN SEA WITH A SOLID ARE OF 20 TO 25 KT WINDS
BETWEEN HISPANIOLA AND COLOMBIA. AN EARLIER QUIKSCAT PASS
CONFIRMED THESE WINDS.

THE ATLANTIC OCEAN...
NOT MUCH HAS CHANGED OVER THE PAST DAY OR TWO. THE SUBTROPICAL
RIDGE CONTINUES TO BUILD WWD ACROSS FLORIDA AND THE EASTERN
GULF. A 1023 MB HIGH CENTER IS LOCATED NEAR 32N57W. THE PRES
GRADIENT IS TIGHTENED BETWEEN THIS HIGH AND THE SEMI-PERMANENT
LOW LOCATED OVER N COLOMBIA. AS A RESULT...20-25 KT TRADE WINDS
ARE BLOWING ACROSS THE CARIBBEAN SEA. ANOTHER 1022 MB HIGH IS
SITUATED NEAR 32N28W. IN BETWEEN...A WEAK SFC TROUGH CLIPS THE
FORECAST AREA NEAR 30N39W.

ALOFT...A DIFFLUENT PATTERN EXISTS ACROSS THE W ATLC. THE
CONTRIBUTING LARGE SCALE FEATURES CONSIST OF A NORTHWESTWARD
MOVING UPPER LOW CENTERED OVER ERN CUBA...AN UPPER HIGH LOCATED
NE OF BERMUDA AND AN ELONGATED UPPER TROUGH OVER THE CENTRAL
ATLC. MUCH OF THE REMAINDER OF THE AREA IS DOMINATED BY AN E-W
RIDGE COVERING THE AREA E OF THE LESSER ANTILLES WITH A MEAN
AXIS ALONG 18N WITH SEVERAL EMBEDDED ANTICYCLONES. THIS RIDGE
AND A CONFLUENT PATTERN...TO THE S OF A LARGE UPPER LOW NEAR SRN
PORTUGAL...IS KEEPING WEATHER CONDITIONS FAIRLY TRANQUIL OUTSIDE
OF THE AREAS OUTLINED ABOVE.

$$
GR



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