[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181805
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT AUG 18 2012

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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1700 UTC.

...SPECIAL FEATURES...

HELENE HAS MOVED INLAND THIS MORNING AND WAS CENTERED NEAR 22.0N
98.5W AT 18/1500 UTC...OR ABOUT 15 MI SSW OF TAMPICO MEXICO...
MOVING NW AT 8 KT. WINDS ASSOCIATED WITH HELENE HAVE DIMINISHED
AND...THE SYSTEM HAS BEEN DOWNGRADED TO A TROPICAL DEPRESSION.
MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB. THE BROAD
CYCLONIC CIRCULATION ASSOCIATED WITH HELENE CONTINUES TO
DOMINATE MUCH OF THE SW GULF S OF 25N AND W OF 93W...WITH
ABUNDANT TROPICAL MOISTURE. SCATTERED TO LOCALLY NUMEROUS
SHOWERS AND TSTMS ARE OCCURRING WITHIN 270 NM ACROSS THE EASTERN
SEMICIRCLE OF THE CENTER OF HELENE...MAINLY OVER WATER. SEE
LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS
MIATCPAT2/WTNT32 KNHC AND THE FULL FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. THE
CIRCULATION ASSOCIATED WITH HELENE IS EXPECTED TO DRIFT W AND NW
OVER THE NEXT FEW DAYS AND WEAKEN...AND INTERACT WITH SIERRA
MADRE ORIENTALES OF MEXICO TO PRODUCE SIGNIFICANT RAINFALL...
WITH THE POTENTIAL FOR WIDESPREAD HEAVY RAINS...LEADING TO AREAS
OF FLASH FLOODING AND MUDSLIDES.

HURRICANE GORDON WAS LOCATED NEAR 34.1N 38.6W AT 18/1500...OR
ABOUT 610 NM WSW OF THE AZORES...MOVING E AT 16 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 983 MB. MAXIMUM SUSTAINED WIND SPEED
HAVE INCREASED TO 70 KT WITH GUSTS TO 85 KT. SATELLITE IMAGERY
THIS MORNING SHOWED A 20 NM WELL DEFINED EYE WITH GORDON. NEARLY
SOLID BANDS WITH NUMEROUS STRONG TSTMS WERE OCCURRING WITHIN 75
NM OF THE CENTER OF GORDON WITH SCATTERED MODERATE CONVECTION
ELSEWHERE WITHIN 150 NM OF CENTER. SEE LATEST NHC INTERMEDIATE
PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT3/WTNT33 AND THE
FULL FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23
KNHC FOR MORE DETAILS. THERE IS SOME OPPORTUNITY FOR GORDON TO
STRENGTHEN SLIGHTLY IN THE NEXT 12 TO 18 HOURS BEFORE INCREASING
WIND SHEAR AND COOLER SST'S CAUSE A STEADY WEAKENING TREND. THE
GOVERNMENT OF PORTUGAL HAS ISSUED A HURRICANE WARNING FOR THE
CENTRAL AND EASTERN AZORES.

A VIGOROUS TROPICAL WAVE IS LOCATED IN THE ERN ATLC ALONG
27W...WITH A ASSOCIATED 1008 MB LOW NEAR 14N27W EMBEDDED WITHIN
THE MONSOON TROUGH. THIS WAVE IS RACING WESTWARD AROUND 20
KT...AND IS NOW FORECAST BY THE GLOBAL MODELS TO MAINTAIN THIS
FAST MOTION ACROSS THE ATLC DURING THE NEXT SEVERAL DAYS.
SCATTERED SHOWERS AND THUNDERSTORMS WERE OCCURRING ARE FROM
11N-16N BETWEEN 27W-31W. CONDITIONS APPEAR CONDUCIVE FOR GRADUAL
DEVELOPMENT DURING THE NEXT FEW DAYS...AND THIS SYSTEM HAS A
MEDIUM CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48
HOURS. GLOBAL MODELS HAS CHANGED SIGNIFICANTLY IN THE FORECAST
OF THIS WAVE DURING THE PAST 2 DAYS...AND A MORE WWD TRAJECTORY
INTO THE CARIBBEAN IS NOW SUGGESTED BY THE OPERATIONAL MODELS AS
WELL AS THE ENSEMBLE MEANS. INTERESTS ACROSS THE E AND NE
CARIBBEAN SHOULD MONITOR THE PROGRESS OF THIS SYSTEM AS IT TREKS
ACROSS THE ATLC.

...TROPICAL WAVES...

A TROPICAL WAVE WAS LOCATED ACROSS THE CENTRAL TROPICAL ATLC
ALONG 41W-42W...WITH AN ASSOCIATED 1013 MB LOW NEAR 11N41W
EMBEDDED WITHIN THE MONSOON TROUGH. THIS WAVE IS MOVING W AT
15-20 KT. SAHARAN AIR CONTINUES TO DOMINATE THIS WAVE AND LIMIT
CONVECTION...WITH SCATTERED MODERATE TO STRONG CONVECTION
OCCURRING ACROSS SRN PORTIONS OF THE LOW...S OF THE MONSOON
TROUGH...AND WELL TO THE NW...FROM 12N TO 15N BETWEEN 42W AND
47W...WHERE NELY FLOW IS CONVERGING. THIS WAVE...AND THE WAVE
MENTIONED ABOVE ALONG 27W...ARE EMBEDDED WITHIN AN ELONGATED
MONSOONAL CIRCULATION THAT EXTENDS FROM THE W COAST OF AFRICA TO
NEAR 50W.

A CARIBBEAN TROPICAL WAVE WAS ALONG ABOUT 70W RACING WWD NEAR 20
KT...WITH SCATTERED MODERATE ISOLATED STRONG CONVECTION
OCCURRING FROM 15N ACROSS HISPANIOLA AND INTO THE ATLC TO
23N...MAINLY BEHIND THE WAVE AXIS BETWEEN 70W AND 67W. ALTHOUGH
THIS WAVE HAS BEEN ACCOMPANIED BY A LARGE AREA OF SAL AS IT HAS
MOVED ACROSS THE ATLC...IT REMAINS VERY ENERGETIC...WITH THE
1200 UTC SAN JUAN UPPER AIR SOUNDING SHOWING SELY WINDS 25-30 KT
IN LAYER FROM JUST ABOVE THE SURFACE TO 1200 FT AGL. THIS WAVE
IS REACHING THE W PERIPHERY OF THE ATLC RIDGE AND WILL BEGIN TO
MOVE MORE WNW THE NEXT FEW DAYS...AND IGNITE WIDELY SCATTERED
MODERATE TO STRONG CONVECTION ACROSS THE N CENTRAL CARIBBEAN AND
GREATER ANTILLES...WITH SAL CONTRIBUTING TO SQUALLS AND STRONG
WIND GUSTS.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXITS THE W AFRICAN COAST NEAR 15N17W...WHERE
THE NEXT TROPICAL WAVE APPEARS POISED TO EXIT THE AFRICAN
CONTINENT THIS AFTERNOON...AND MEANDERS WWD TO LOW PRES 1008 MB
NEAR 14N27W...THEN CONTINUES WSW TO LOW PRES NEAR 11N42W...THEN
CONTINUES ON TO 09N52W...WHERE IT TRANSITIONS TO
ITCZ...CONTINUING ON TO 08N59W TO 11N67W. CONVECTION ASSOCIATED
WITH THE TROUGH IS ADEQUATELY DESCRIBED ABOVE WITH EACH OF THE
TROPICAL WAVES. SCATTERED MODERATE TO STRONG CONVECTION
ASSOCIATED WITH THE WAVE ALONG THE W COAST OF AFRICA WAS
OCCURRING FROM 11N-15N E OF 21W. SCATTERED MODERATE TO STRONG
CONVECTION ASSOCIATED WITH THE ITCZ WAS OCCURRING ALONG COASTAL
SECTIONS OF GUYANA AND VENEZUELA BETWEEN 59W AND 66W.

...DISCUSSION...

GULF OF MEXICO...
WEAK SURFACE RIDGING EXTENDS FROM THE W ATLC ACROSS SRN FLORIDA
AND INTO THE CENTRAL GULF...THEN NW INTO THE NW GULF...AS HELENE
SLOWLY DRIFTS FURTHER INLAND ACROSS MEXICO. A WEAK SURFACE
TROUGH WAS BEGIN DRAGGED EWD ACROSS N CENTRAL FLORIDA...YIELDING
MOISTURE CONVERGENCE TO ITS S ACROSS CENTRAL PORTIONS OF THE
STATE WITH SCATTERED MODERATE CONVECTION. A WEAK COLD FRONT WAS
SINKING SWD ACROSS THE N GULF STATES WITH NUMEROUS MODERATE TO
STRONG CONVECTION ERUPTING ACROSS S LOUISIANA AND THE NEARSHORE
COASTAL WATERS...AND IS EXPECTED TO SHIFT SLOWLY ESE THIS
AFTERNOON. BROAD UPPER TROUGHING ACROSS THE E TWO-THIRDS OF THE
US.S WILL MAINTAIN MILD W TO NW FLOW ALOFT ACROSS THE N AND NE
GULF AND YIELD UNSTABLE CONDITIONS...AND THUS ACTIVE CONVECTION
IS EXPECTED THERE THROUGH THIS EVENING. ACROSS THE SW AND S
CENTRAL GULF...MOIST AND UNSTABLE SELY FLOW CONTINUES TO SPREAD
MOISTURE TOWARDS TEXAS AND THE MEXICAN OFFSHORE WATERS. SE WINDS
15-20 KT WITH SEAS 6-7 FT ARE LIKELY TO CONTINUE ACROSS THIS
REGION THROUGHOUT THE DAY.

CARIBBEAN SEA...
SCATTERED TO NUMEROUS MODERATE TO STRONG CONVECTION WAS SHIFTING
W ACROSS THE SW CARIBBEAN S OF 12.5W AND W OF 76W...AND APPEARS
TO BE ASSOCIATED WITH A WEAK PERTURBATION ALONG THE MONSOON
TROUGH INTERACTING WITH DIVERGENT UPPER SW FLOW. SKIES WERE
GENERALLY CLEAR ACROSS THE REMAINDER OF THE BASIN W OF THE
TROPICAL WAVE ALONG 70W...WITH SPOTTY CONVECTION S OF CUBA. ITCZ
RELATED MOISTURE IS BEGIN DRAGGED WWD ACROSS VENEZUELA BEHIND
THE TROPICAL WAVE ALONG 70W...AND SAL AND VERY STABLE AIR
FOLLOWING THIS WAVE AND MOVING INTO THE E CARIB ATTM. SQUALLS
AND TSTMS ASSOCIATED WITH THIS WAVE WILL EXT THE WATERS OF THE
MONA PASSAGE LATER THIS AFTERNOON AND CONTINUE TO AFFECT
HISPANIOLA AND THE ADJACENT WATERS. FRESH SE WINDS AROUND 20 KT
WILL OCCUR WITH AND BEHIND THIS WAVE...MAINLY N OF 15N...WITH
SEAS 5-7 FT. OTHERWISE MODERATE TRADEWINDS PREVAIL ACROSS THE
BASIN.

ATLANTIC OCEAN...
WATER VAPOR SHOWS A VERY BROAD UPPER LEVEL TROUGH ACROSS THE E
TWO-THIRDS OF THE U.S. SHIFTING SLOWLY E OFF THE ERN SEABOARD.
CONVERGENCE LINES BETWEEN BERMUDA AND THE SE U.S. COAST ARE
RESPONDING FAVORABLE TO THIS UNSTABLE ENVIRONMENT TO YIELD
BROKEN LINES OF WIDELY SCATTERED SHOWERS AND TSTMS. A TUTT
STRETCHED SW TO NE FROM HISPANIOLA TO THE CENTRAL ATLC AND IS
PRODUCING A GENERALLY STABLE ATMOSPHERE N OF 20N E OF 60W. SAL
ASSOCIATED WITH THE THREE TROPICAL WAVES DISCUSSED ABOVE IS
SPREAD ACROSS MUCH OF THE TROPICAL AND SUBTROPICAL ATLC FROM NW
AFRICA W-SW INTO THE ERN CARIB...AND IS MOST DENSE N OF THE
WAVES...N OF 16N. GOES-R PRODUCTS CLEARLY SHOW THIS SAL...WITH A
VERY NARROW BREAK N OF 16N ALONG 42-43W. A THERMAL LOW PRES
CENTER ALONG THE W COAST OF AFRICA NEAR 20N17W CONTINUES TO
ENTRAIN DENSE AFRICAN DUST THAT STRETCHES N-NE ALONG THE COAST
AND INTO SW PORTIONS OF SPAIN.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
STRIPLING





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