[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 170001
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI SEP 16 2005

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM
THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON
SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND
METEOROLOGICAL ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...

TROPICAL STORM OPHELIA CENTERED NEAR 37.4N 72.6W...OR 260 NM SSW
OF NANTUCKET MASSACHUSETTS...AT 17/0000 UTC MOVING NE 14 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 993 MB. MAXIMUM SUSTAINED
WIND SPEED IS 55 KT WITH GUSTS TO 65 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC
AND THE PUBLIC ADVISORY UNDER HEADERS MIATCPAT1/WTNT31 KNHC FOR
MORE DETAILS. CONVECTIVE TOPS HAVE WARMED WITH OPHELIA AND THE
SW SIDE OF THE SYSTEM HAS DEVELOPED A SHARP APPEARANCE AS IT
BEGINS TO FEEL THE EFFECTS TO THE MID-LATITUDE WESTERLIES AND
STRONGER SHEAR. IN FACT...THE HEAVIEST CONVECTION APPEARS TO BE
SHIFTING TO THE NE SIDE OF THE LOW-LEVEL CIRCULATION. SCATTERED
SHOWERS/TSTMS FROM 36N-40N BETWEEN 69W-73W. WSR-88D IMAGERY FROM
DOVER DELAWARE FAINTLY SHOWS SHOWERS ROTATING AROUND THE N SIDE
OF THE PERCEIVED CENTER BUT THE STRONGEST CONVECTION IS LOCATED
E OF THIS FEATURE.

A TROPICAL DISTURBANCE...1009 MB LOW...IS CENTERED ABOUT 400 NM
ESE OF BARBADOS NEAR 11.5N53W MOVING WNW 10-15 KT...ALONG THE
TROPICAL WAVE NEAR 52W/53W. VISIBLE IMAGERY INDICATES THAT THE
CIRCULATION AROUND THE SURFACE LOW IS BECOMING MORE CONSOLIDATED
AND IS ISOLATING ITSELF FROM THE ITCZ AXIS AND A SEPARATE SWIRL
ABOUT 400 NM TO THE N. THE SYSTEM IS EMBEDDED IN A BROAD
DIFFLUENT UPPER LEVEL ENVIRONMENT AND THESE CONDITIONS ARE
EXPECTED TO PERSIST FOR THE NEXT SEVERAL DAYS. TROPICAL CYCLONE
DEVELOPMENT IS POSSIBLE JUST E OF THE LESSER ANTILLES WITHIN THE
NEXT 36 HRS...WITH HEAVY SHOWERS/TSTMS EXPECTED TO SPREAD OVER
THE ISLANDS LATER ON SAT AND SUN. NUMEROUS MODERATE/ISOLATED
STRONG CONVECTION FROM 10N-13N BETWEEN 47W-56W.

AN AREA OF SHOWERS/TSTMS EXTENDING UP TO 350 NM N OF PUERTO RICO
AND THE VIRGIN ISLANDS IS BEING PRODUCED BY A COMBINATION OF A
TROPICAL WAVE MOVING ACROSS THE E CARIBBEAN...THE SRN EXTENT OF
AN OLD FRONTAL BOUNDARY...AND AN UPPER LEVEL LOW CENTERED N OF
HISPANIOLA NEAR 23N70W. THE CONVECTION LIES ON THE DIFFLUENT E
SIDE OF THE UPPER LOW AND IS BEING FORCED BY SEVERAL LOW-LEVEL
BOUNDARIES WHICH ARE BEING OBSCURED BY CLOUD COVER. A SURFACE
LOW HAS NOT DEVELOPED AS OF YET...BUT THIS COULD OCCUR SOON IF
THE CONVECTION CAN BE MAINTAINED FOR A PROLONGED PERIOD OF TIME.
ASSUMING THE LOW WILL DEVELOP...TROPICAL CYCLONE DEVELOPMENT
WILL BE POSSIBLE IN AN AREA FROM N OF THE VIRGIN ISLANDS INTO
THE EXTREME SRN BAHAMAS WITHIN THE NEXT 36 HRS. WIDELY SCATTERED
MODERATE CONVECTION FROM 19N-23N BETWEEN 60W-68W.

...TROPICAL WAVES...

EAST ATLANTIC TROPICAL WAVE ALONG 27W/28W S OF 17N MOVING W 10
KT. THE LAST FEW VISIBLE MET-8 IMAGES OF THE DAY SHOW A LOW
AMPLITUDE BUT WELL-DEFINED AND SHARP SIGNATURE ABOUT 200-250 NM
SW OF THE CAPE VERDE ISLANDS. THERE MAY BE A WEAK LOW ALONG THE
WAVE BUT WHATEVER LOW-LEVEL CIRCULATION THERE MAY BE APPEARS
STRETCHED FROM SW TO NE. SCATTERED MODERATE/STRONG CONVECTION IS
MAINLY AHEAD OF THE WAVE NEAR THE ITCZ FROM 4N-10N BETWEEN
27W-34W. WIDELY SCATTERED SHOWERS/TSTMS ELSEWHERE FROM 7N-16N
BETWEEN 22W-28W.

SEE SPECIAL FEATURES FOR TROPICAL WAVE/LOW ALONG 52W/53W.

TROPICAL WAVE CROSSING THE LESSER ANTILLES ALONG 63W S OF 21N
MOVING W 10-15 KT. SURFACE OBSERVATIONS FROM GUADELOUPE SWD TO
TOBAGO SHOW MAINLY LIGHT SE FLOW BEHIND THE WAVE AXIS...AND OBS
FROM ANGUILLA AND THE U.S. AND BRITISH VIRGIN ISLANDS SHOW LIGHT
NE FLOW AHEAD OF THE AXIS. THE NRN PART OF THE WAVE IS
INTERACTING WITH A SMALL UPPER LOW LOCATED ONLY ABOUT 80 NM N OF
THE VIRGIN ISLANDS AND IS PRODUCING SCATTERED SHOWERS/TSTMS WITH
EMBEDDED ISOLATED MODERATE CONVECTION FROM 18N-24N BETWEEN
59W-65W...PREDOMINANTLY NE OF THE ISLANDS AT THIS TIME.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 10N10W 10N18W 15N25W...THEN ALONG
8N28W 6N35W 17N48W...THEN ALONG 10N54W 14N60W. SCATTERED
MODERATE CONVECTION FROM THE GUINEA-BISSAU/GUINEA BORDER SWD TO
LIBERIA DRIFTING UP TO 90 NM OFFSHORE. NUMEROUS MODERATE/STRONG
ASSOCIATED WITH TROPICAL WAVE 28W FROM 4N-9N BETWEEN 26W-34W.
SCATTERED SHOWERS/TSTMS WITHIN 100 NM OF THE AXIS BETWEEN
37W-42W. SCATTERED MODERATE WITHIN 100 NM OF THE AXIS BETWEEN
44W-50W.

...DISCUSSION...

GULF OF MEXICO...
A STRONG UPPER LEVEL HIGH IS CENTERED OVER THE RIO GRANDE VALLEY
NEAR 29N101W WITH AN ASSOCIATED RIDGE AXIS STRETCHING FROM SRN
ALABAMA TO THE GULF OF CALIFORNIA. THE HIGH IS DRIVING MODERATE
N/NE FLOW INTO THE N GULF...THEN WWD TOWARDS THE MEXICAN COAST
WITH DRY AIR INFILTRATING ACROSS MOST OF THE AREA. A WEAK
COLD/STATIONARY FRONT ACROSS CNTRL TEXAS AND NRN LOUISIANA IS
PRODUCING WIDELY SCATTERED TSTMS ACROSS THE GULF COAST STATES
FROM HOUSTON TO ATLANTA...BUT RELATIVELY LITTLE OF THIS ACTIVITY
IS MOVING OFFSHORE. A VIGOROUS UPPER LEVEL LOW IS LOCATED S OF
THE RIDGE OVER THE ISTHMUS OF TEHUANTEPEC NEAR 18N95W...MOVING
WSW 15 KT...AND IS DRAWING TROPICAL MOISTURE NWD OVER THE
YUCATAN PENINSULA WITH NUMEROUS MODERATE CONVECTION DEVELOPING
FROM 15N-21.5N BETWEEN 88W-92W. THE WEEKEND LOOKS TO BE MAINLY
DRY ACROSS THE AREA...WITH ONLY OCCASIONALLY SHOWERS FOCUSED
OVER THE NW GULF AHEAD OF THE DYING FRONTAL BOUNDARY AND OVER
THE BAY OF CAMPECHE WHERE MOISTURE IS MOST CONCENTRATED.

CARIBBEAN...
WITH THE STRONG UPPER LOW DEPARTING TO THE W OVER SRN MEXICO...A
SEGMENT OF THE LEFTOVER TROUGH STRETCHES FROM BELIZE TO THE
CAYMAN ISLANDS AND JAMAICA. THIS FEATURE IS KEEPING THE DEEPEST
TROPICAL MOISTURE LOCATED TO THE S WITH SCATTERED MODERATE
CONVECTION DEVELOPING FROM GUATEMALA EWD TO HONDURAS AND NRN
NICARAGUA. ISOLATED TSTMS SURROUND OTHER QUADRANTS OF THE
LOW...INCLUDING OVER JAMAICA AND W CUBA WHERE DAYTIME
INSTABILITY WAS GREATEST. A DIFFLUENT UPPER HIGH OVER THE SW
CARIBBEAN NEAR 12N80W HAD BEEN SUPPORTING A LARGE CLUSTER OF
CONVECTION N OF PANAMA...BUT THIS AREA HAS BEEN COLLAPSING WITH
ONLY SCATTERED SHOWERS/TSTMS NOW S OF 14N BETWEEN 77W-83W.
FARTHER E...A BROAD UPPER TROUGH HAS CARVED SWD TO THE VENEZUELA
COAST E OF 76W WITH A SWATH OF MODERATE/STRONG SUBSIDENCE S OF
16N. SCATTERED TSTMS HAVE BEEN ONGOING OVER HISPANIOLA AND NEAR
PUERTO RICO...AND ACCOMPANYING THE TROPICAL WAVE ALONG 52W...BUT
OTHERWISE THE E/CNTRL CARIBBEAN IS UNDER RELATIVELY FAIR SKIES.
HOWEVER...THE TROPICAL DISTURBANCE E OF THE ISLANDS MAY BRING
MORE INCLEMENT WEATHER TO PARTS OF THE REGION BY LATER IN THE
WEEKEND AS IT MOVES GENERALLY NW.

ATLANTIC...
A BROAD UPPER LOW CENTERED NEAR 23N71W IS MOVING W TOWARDS THE
SRN BAHAMAS 10-15 KT AND IS DRAGGING DRY AIR FROM OVER THE W
ATLC WATERS TOWARDS THE BAHAMAS AND FLORIDA. HOWEVER...THE
DIFFLUENT E SIDE OF THE LOW HAS BEEN FOSTERING CONVECTIVE
DEVELOPMENT N OF PUERTO RICO AND IT IS POSSIBLE THAT A SURFACE
LOW...OR TROPICAL CYCLONE...MAY DEVELOP OVER THE NEXT FEW DAYS N
OF HISPANIOLA. FARTHER E...A WEAK UPPER LOW IS CENTERED NEAR
32N52W WITH A TROUGH EXTENDING SW TO 27N63W AND A 60 KT
WESTERLY JET EMANATING E OF THE SUSPECT AREA INTO THE CENTRAL
ATLC. THIS IS PRODUCING STRONG WESTERLY SHEAR OVER THE CENTRAL
ATLC BETWEEN 16N-26N...BUT THE TROPICAL DISTURBANCE E OF THE
LESSER ANTILLES IS TOO FAR S TO BE AFFECTED BY THIS ENVIRONMENT.
AN OLD FRONTAL BOUNDARY EXTENDS NE AND INTO THE TSTMS N OF
PUERTO RICO ALONG 31N45W 26N60W WITH ISOLATED SHOWERS/TSTMS
WITHIN 60 NM OF THE BOUNDARY BETWEEN 50W-59W. AN UPPER HIGH IS
CENTERED OVER THE E ATLC NEAR 12N40W WITH A RIDGE EXTENDING WWD
ACROSS THE TROPICAL DISTURBANCE AND EWD TO NEAR 11N30W. BROAD
DIFFLUENCE ON THE SE SIDE OF THE RIDGE IS ALSO FOSTERING
CONVECTIVE DEVELOPMENT WITH THE TROPICAL WAVE ALONG 28W DEEP
INTO THE TROPICS. THE UPPER FLOW OVER THE SUBTROPICAL E ATLC IS
GENERALLY LIGHT AND VARIABLE...BUT THERE IS A WEAK TROUGH ALONG
30N17W 21N34W THAT IS DRAWING MOISTURE NWD FROM SENEGAL INTO
WESTERN SAHARA AND ALGERIA.

$$
BERG



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