[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 101751
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON SEP 10 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
1715 UTC.

...SPECIAL FEATURE...
TROPICAL DEPRESSION GABRIELLE CONTINUES TO MOVE AWAY FROM THE
UNITED STATES. AS OF 10/1500 UTC THE CENTER OF THE DEPRESSION
WAS NEAR 37.1N 73.0W OR ABOUT 285 NM SOUTH-SOUTHWEST OF
NANTUCKET MASSACHUSETTS. GABRIELLE IS MOVING EAST-NORTHEAST AT
11 KT. MAXIMUM SUSTAINED WINDS REMAIN 30 KT WITH GUSTS TO 40 KT.
THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1009 MB. PLEASE REFER
TO THE NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT2/WTNT22 KNHC AND/OR THE PUBLIC ADVISORY
MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. DURING THE PAST SEVERAL
HOURS A SMALL AREA OF THUNDERSTORMS HAS DEVELOPED ABOUT 75 NM
SOUTHEAST OF THE CENTER. HOWEVER...NORTHWESTERLY SHEAR HAS NOT
ALLOWED THIS THUNDERSTORM ACTIVITY TO ACQUIRE MUCH CURVATURE.
THE NHC OFFICIAL FORECAST WILL MAINTAIN THE CYCLONE AS A 30 KT
DEPRESSION UNTIL IT MERGES WITH A LARGER EXTRATROPICAL LOW IN
ABOUT 48 HOURS. GABRIELLE IS EXPECTED TO PASS WELL SOUTH OF THE
COAST OF THE NORTHEASTERN UNITED STATES.

...TROPICAL WAVES...

TROPICAL WAVE IS JUST EAST OF THE CAPE VERDE ISLANDS ALONG 22W
S OF 19N MOVING W 10-15 KT. ALTHOUGH A BROAD CYCLONIC TURNING IS
SEEN OF SFC DATA...THE WAVE LOOKS FAIRLY DISORGANIZED ON
SATELLITE IMAGERY. AN EARLIER QUIKSCAT PASS DID NOT SHOW A SFC
CLOSED CIRCULATION AND THE ASCAT MISSED THE SYSTEM. SCATTERED
MODERATE CONVECTION IS CONFINED TO AN AREA W OF THE AXIS FROM
10N-17N BETWEEN 22W-26W.

AN ACTIVE TROPICAL WAVE IS ALONG 40W/41W S OF 16N. THIS SYSTEM
WAS SLIGHTLY ADJUSTED AHEAD BASED ON SATELLITE IMAGERY AND THE
POSITION OF THE SFC LOW ALONG THE WAVE AXIS...WHICH IS NEAR
9N41W WITH 1010 MB. IT IS PRODUCING A LARGE AREA OF CLOUDINESS
AND THUNDERSTORMS. THIS SYSTEM IS GRADUALLY BECOMING BETTER
ORGANIZED AND HAS THE POTENTIAL TO DEVELOP INTO A TROPICAL
DEPRESSION DURING THE NEXT COUPLE OF DAYS AS IT MOVES WESTWARD
TO WEST-NORTHWESTWARD AT 10-15 MPH.

TROPICAL WAVE IS OVER THE LESSER ANTILLES ALONG 61W S OF 20N.
A BURST OF CONVECTION HAS DEVELOPED ON THE NORTHERN SIDE OF THE
WAVE FROM 14N-18N BETWEEN 60W-63W. THIS WAVE SHOWS UP FAIRLY
WELL IN THE SHIP/BUOY DATA AND SATELLITE PHOTOS. THE WAVE IS
GENERATING MAINLY LIGHT SHOWERS AND TSTMS OVER THE ISLANDS...
PARTICULARLY BETWEEN MARTINIQUE AND ANTIGUA. SIGNIFICANT
DEVELOPMENT OF THIS SYSTEM IS NOT EXPECTED AS IT MOVES
WEST-NORTHWESTWARD AT ABOUT 15 MPH. MOISTURE FROM THIS WAVE WILL
AFFECT THE UK/US VIRGIN ISLANDS AND PUERTO RICO THIS EVENING AND
TONIGHT.

THE NRN PORTION OF A TROPICAL WAVE ALONG 94W EXTENDS INTO THE
BAY OF CAMPECHE S OF 20N MOVING W 10-15 KT. THERE IS A FAIR
AMOUNT OF MOISTURE IN THIS AREA. HOWEVER...IT IS DIFFICULT TO
TELL HOW MUCH OF THIS IS RELATED TO THE WAVE ITSELF AS THERE IS
A WELL DEFINED UPPER TROUGH AND LOW-LEVEL TROUGHING IN THIS
GENERAL AREA AS WELL. MORE ON THIS IN THE GULF OF MEXICO SECTION
BELOW.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N13W 9N21W 10N35W 8N45W 10N60W.
BESIDES FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...
CLUSTERS OF SCATTERED MODERATE/ ISOLATED STRONG CONVECTION ARE
WITHIN 100 NM N OF AXIS WEST OF 50W.

DISCUSSION...

THE GULF OF MEXICO...
A LARGE BUT DISORGANIZED AREA OF CLOUDINESS AND THUNDERSTORMS IS
OVER THE CENTRAL AND SOUTHWESTERN GULF OF MEXICO. SEVERAL
FEATURES ARE ENHANCING THIS CONVECTIVE ACTIVITY. THEY ARE...A
SFC TROUGH THAT RUNS FROM THE MOUTH OF THE MISSISSIPPI TO A
1011MB LOW LOCATED NEAR 23N93W...THE NORTHERN EXTENSION OF A
TROPICAL WAVE ALONG 94W/95W...AND AN UPPER LOW LOCATED ALONG THE
MEXICAN COAST BETWEEN TAMPICO AND VERACRUZ. CONDITIONS DO NOT
APPEAR FAVORABLE FOR SIGNIFICANT DEVELOPMENT OF THIS SYSTEM AS
IT MOVES SLOWLY WESTWARD OR WEST-NORTHWESTWARD DURING THE NEXT
DAY OR TWO. SAT IMAGES AND LIGHTNING DATA REVEAL POCKETS OF
SCATTERED SHOWERS AND TSTMS...IN THIS MOIST AND UNSTABLE
ENVIRONMENT. AN UPPER RIDGE DOMINATES THE N GULF WATERS
SUPPORTING FAIR WEATHER. THE GFS MODEL MOVES ALL THIS MOISTURE
NWD MERGING WITH A NEW TROUGH OR WEAK FRONT THAT IS EXPECTED TO
PUSH OFF THE TEXAS COAST WED. THIS WILL ALLOW THE SFC PATTERN TO
REMAIN WEAK KEEPING WINDS MOSTLY LIGHT.

THE CARIBBEAN SEA...
A TROPICAL WAVE IS JUST ENTERING THE BASIN PRODUCING SCATTERED
SHOWERS AND TSTMS OVER THE LESSER ANTILLES. SEE THE TROPICAL
WAVE SECTION ABOVE. SCATTERED MODERATE CONVECTION IS ALONG THE
ATLANTIC COAST OF NICARAGUA AND THE SW CARIBBEAN. A DIFFLUENT
PATTERN ALOFT BETWEEN A WEAK UPPER HIGH OVER CENTRAL AMERICA AND
AN UPPER LOW COVERING THE E CARIBBEAN IS HELPING TO DEVELOP THIS
CONVECTIVE ACTIVITY. ELSEWHERE...TYPICAL TRADE WIND SHOWERS ARE
SEEN. MODERATE TRADE WINDS ARE BLOWING ACROSS THE REGION WITH 20
KT WINDS CONFINED TO NEAR THE COLOMBIAN COAST. THESE WINDS ARE
ANTICIPATED TO INCREASE E OF 75W OVER THE NEXT COUPLE OF DAYS AS
THE GRADIENT TIGHTENS BETWEEN RIDGE N OF AREA AND THE COLOMBIAN
LOW.

THE ATLANTIC OCEAN...
A LARGE NEARLY STATIONARY VERTICALLY STACKED LOW PRES SYSTEM IS
LOCATED WELL N OF THE AREA IN THE CENTRAL ATLC. TWO WEAK
ASSOCIATED SFC TROUGHS STRETCH THROUGH THE AREA. THE MAIN OLD
FRONTAL BOUNDARY ENTERS THE AREA NEAR 32N37W AND EXTENDS MAINLY
SW ALONG 25N50W 24N65W...THEN CONTINUES NW AND N TO 28N68W. THE
TROUGH IS PRETTY ACTIVE WEST OF 55W...WHERE SAT PICTURES SHOWS A
50-60 NM WIDE BAND OF SHOWERS AND TSTMS. A POST-FRONTAL BOUNDARY
WITH MUCH LESS SHOWER ACTIVITY IS CLIPPING THE AREA ALONG 30N
BETWEEN 46W AND 57W. THIS WEATHER PATTERN KEEPS THE SFC WINDS
VERY LIGHT ACROSS THE BULK OF THE CENTRAL ATLC. MODERATE TRADE
WINDS ARE FOUND SOUTH OF 20N. A 1022 MB HIGH IS NEAR 32N64W WITH
A RIDGE EXTENDING OVER THE W ATLC AND THE STATE OF FLORIDA.

ALOFT...A RIDGE/TROUGH/RIDGE DOMINATES THE FORECAST AREA. A
RIDGE...ANCHORED ON A HIGH OVER THE SE U.S. COVERS MOST OF THE W
ATLC. AN INVERTED TROUGHING IS ALONG 65W/66W S OF 23N. FARTHER
EAST...THERE IS A DEEP LAYERED TROUGH THAT SUPPORTS THE
AFOREMENTIONED SFC TROUGHS. AN UPPER HIGH LOCATED N OF THE CAPE
VERDE ISLANDS NEAR 22N25W IS IN CONTROL OF THE REMAINDER OF THE
AREA PROVIDING FAIR WEATHER.

OF NOTE...TODAY MARKS THE CLIMATOLOGICAL PEAK OF THE HURRICANE
SEASON. SO FAR...THE ONLY HURRICANES THAT HAVE FORMED...DEAN
AND FELIX...BECAME CATEGORY FIVE HURRICANES ON THE
SAFFIR-SIMPSON SCALE. IN ADDITION BOTH DEAN AND FELIX MADE
LANDFALL AS CATEGORY FIVE HURRICANES WITH SUSTAINED WINDS OF
NEAR 145 KT AND 140 KT RESPECTIVELY. THIS REPRESENTS THE FIRST
TIME THAT TWO CATEGORY FIVE HURRICANES HAVE MADE LANDFALL IN THE
ONE SEASON.

$$
GR




This weather bulletin was brought to you by:
www.nashvilleweather.net