[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 280004
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT AUG 27 2011

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2200 UTC.

...SPECIAL FEATURE...
THE CENTER OF HURRICANE IRENE WAS LOCATED NEAR 36.2N 76.0W AT
2100Z...OR ABOUT ABOUT 50 MI SSE OF NORFOLK VIRGINIA AND ABOUT
340 MI SSW OF NEW YORK CITY...MOVING TOWARD THE NORTH-NORTHEAST
OR 15 DEGREES AT 11 KT. MINIMUM CENTRAL PRESSURE WAS ESTIMATED
AT 950 MB. MAXIMUM SUSTAINED WIND SPEED WAS 70 KT WITH GUSTS TO
85 KT. PLEASE SEE THE LATEST INTERMEDIATE PUBLIC ADVISORY UNDER
AWIPS/WMO HEADER MIATCPAT4/WTNT34 KNHC AND THE FULL
FORECAST/ADVISORY UNDER AWIPS/WMO HEADER MIATCMAT4/WTNT24 KNHC
FOR MORE DETAILS. THE CENTER OF IRENE WAS MOVING ACROSS
CURRITUCK SOUND ACROSS FAR NE NORTH CAROLINA...WITH THE E HALF
OF THE CORE CIRCULATION MOVING OVER THE COAST AND IMMEDIATE
COASTAL WATERS. RAINBANDS WITH NUMEROUS MODERATE TO STRONG
CONVECTION WERE OCCURRING WITHIN 90 NM ACROSS THE NE AND 30 NM
SW SEMICIRCLES...WHILE VERY LONG RAINBANDS WITH NUMEROUS
MODERATE ISOLATED STRONG CONVECTION WERE OCCURRING FROM NEW
JERSEY AND SOUTHEAST PENNSYLVANIA AND SPIRALING SOUTHWEST AND
THEN SOUTH ACROSS MARYLAND...VIRGINIA AND INTO EASTERN NORTH
CAROLINA...ALL LEAVING VERY HEAVY TO TORRENTIAL RAINFALL. IRENE
IS FORECAST TO MOVE NNE ACROSS THE COASTAL WATERS OF
VIRGINIA...MARYLAND AND DELAWARE IN THE NEXT 6 TO 8 HOURS AND
THEN BEGIN TO ACCELERATE SUNDAY MORNING AS IT BRUSHES THE NEW
JERSEY COASTLINE AND MOVES ASHORE FOR GOOD ACROSS PORTIONS OF
LONG ISLAND NEW YORK. SOME GRADUAL WEAKENING IS EXPECTED
OVERNIGHT...WITH IRENE EXPECTED TO REACH COASTAL NEW YORK AT
JUST UNDER HURRICANE STRENGTH.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH IS ANALYZED MEANDERING ACROSS THE SAHARAN
DESERT THEN SW TO THE COASTAL WATERS OF GUINEA-BISSAU TO A
DEVELOPING 1011 MB SURFACE LOW NEAR 10N17W ASSOCIATED WITH A
TROPICAL WAVE THAT HAS MOVED OFF THE COAST OF AFRICA. NUMEROUS
MODERATE TO STRONG CONVECTION WAS OCCURRING FROM 06N TO 11N
BETWEEN 19W AND 23W. A 1011 MB LOW...REMNANTS OF T.D. TEN...WAS
CENTERED NEAR 17.5N35W MOVING SLOWLY NW WITH A SURFACE TROUGH
EXTENDING NE TO SW THROUGH THE LOW FROM 23N31W TO 11N43W TO
TON48W WHERE IT TRANSITIONED TO ITCZ ALONG 09.5N55W TO COASTAL
VENEZUELA AT 08N60W. SCATTERED MODERATE ISOLATED STRONG
CONVECTION WAS OCCURRING S OF THE TROUGH IN THE CONFLUENT LLVL
SWLY FLOW FROM 09N TO 12N BETWEEN 36W AND 47W. A WEAK WAVE HAS
DEVELOPED OVER THE PAST FEW DAYS IN LIGHT TRADEWIND FLOW E OF
THE LESSER ANTILLES...AND WAS ALONG 59W FROM ABOUT 10N TO 16N
AND DRIFTING W...WITH GOOD LLVL CONVERGENCE BETWEEN 13N AND 16N
MAINTAINING ACTIVE MODERATE TO STRONG CONVECTION BETWEEN 56W AND
61W.

...DISCUSSION...

GULF OF MEXICO...
A MIDDLE TO UPPER LEVEL TROUGH LINGERS ACROSS THE NRN GULF FROM
CENTRAL GEORGIA TO THE S TIP OF TEXAS WITH A NEW SHORTWAVE
DIVING S ACROSS THE MS VALLEY POISED TO REINFORCE THIS TROUGH IN
THE NEXT 24 HOURS. THIS IS YIELDING CONVERGENCE ALOFT N OF
27.5N. MILD W TO NW FLOW ALOFT PREVAILS ACROSS THE BASIN S OF
THE NEARLY E TO W UPPER TROUGH...YIELDING MODEST DIVERGENCE
ACROSS W PORTIONS ALONG 23N WERE SCATTERED SMALL TSTMS THAT
DOTTED THE WATERS W OF 94.5W THIS AFTERNOON HAVE DIMINISHED. A
WEAK 1013 MB HIGH WAS ANALYZED ACROSS THE NW GULF NEAR 26.5N94W
THIS AFTERNOON AND WAS DEPICTED IN A 1536Z ASCAT PASS. LIGHT TO
MODERATE WLY SFC FLOW PREVAILS N THROUGH E OF THIS HIGH TO THE
FLORIDA PENINSULA...WITH LIGHT AND VARIABLE FLOW ACROSS THE SW
GULF. DIURNAL CONVECTION HAS FLARED ACROSS THE YUCATAN PENINSULA
YIELDING NUMEROUS SHOWERS AND TSTMS THAT WILL SHIFT W INTO THE
SW GULF DURING THE EVENING HOURS AND DIMINISH VERY SLOWLY
OVERNIGHT. A MID LEVEL WEAKNESS EXISTS JUST OFFSHORE OF THE W
COAST OF THE YUCATAN PENINSULA AND IS FORECAST TO BECOME
SOMEWHAT BETTER ORGANIZED IN THE NEXT FEW DAYS. THIS WILL
MAINTAIN LOW TO MID LEVEL CONVERGENCE AND INSTABILITY ACROSS THE
E HALF OF THE BAY OF CAMPECHE AND LARGE PORTIONS OF THE YUCATAN
PENINSULA LEADING TO PERIODS OF ACTIVE CONVECTION.

CARIBBEAN SEA...
A MID TO UPPER LEVEL CYCLONE OF THE W CENTRAL ATLC EXTENDS A
TROUGH SW ACROSS PUERTO RICO THEN S TO NEAR 13N67W. UPPER
CONVERGENCE WAS OCCURRING TO THE NW OF THE AXIS ACROSS PUERTO
RICO AND THE MONA PASSAGE WHILE SPEED DIVERGENCE WAS FOUND TO
THE SE OF THE AXIS. WIDESPREAD AFTERNOON CONVECTION OCCURRING
ACROSS THE SE CARIBBEAN SE OF THE TROUGH HAS DIMINISHED
CONSIDERABLY RECENTLY AND WAS MORE ISOLATED AT 2200Z. AN
ELONGATED RIDGE EXTENDED FROM THE W ATLC E OF IRENE SW TO AN
UPPER ANTICYCLONE OVER THE NW CARIBBEAN...AND WAS YIELDING N TO
NE FLOW ALONG ACROSS THE CENTRAL CARIBBEAN BETWEEN 69W AND 81W.
A WEAK LOW LEVEL PERTURBATION ACROSS THE CENTRAL CARIBBEAN FROM
COLOMBIA NNE TO S OF HISPANIOLA WAS TRANSPORTING A BROAD AREA OF
ABUNDANT LOW LEVEL MOISTURE N AND NW THAT HAS RECENTLY IGNITED
INTO SCATTERED TO NUMEROUS MODERATE CONVECTION. MILD DIRECTIONAL
DIFFLUENCE ALOFT ACROSS THIS AREA WAS VENTING THIS CONVECTION
NICELY. THIS PERTURBATION IS FORECAST TO SHIFT WNW IN THE NEXT
FEW DAYS AND MAY BECOME BETTER ORGANIZED AS IT MOVES ACROSS THE
SW PERIPHERY OF THE STRENGTHENING ATLC RIDGE. PRESENTLY...WEAK
ANTICYCLONIC FLOW PREVAILS AT THE SFC ACROSS THE CARIBBEAN...
WITH MODERATE E TO SE WINDS ACROSS THE EAST AND CENTRAL PORTIONS
BECOMING LIGHT SE TO S ACROSS NW AND W PORTIONS. AS IRENE LIFTS
FURTHER TO THE N AND NE DURING THE NEXT FEW DAYS LOOK FOR THE
ATLC RIDGE TO BUILD BACK IN ACROSS THE BASIN AND BRING A RETURN
TO MORE TYPICAL TRADEWINDS.

ATLANTIC OCEAN...
THE PRIMARY FOCUS ACROSS THE ATLC TODAY CONTINUES TO BE
HURRICANE IRENE. FOR MORE INFORMATION ON IRENE...SEE SPECIAL
FEATURES ABOVE. THE BROAD CYCLONIC WIND FIELD ENCOMPASSES THE NE
GULF TO THE SW N ATLC ALONG ABOUT 69-70W...AND IS DRAWING
TROPICAL MOISTURE FROM THE CARIBBEAN AND CENTRAL ATLC NWD ACROSS
THE BAHAMAS AND SW N ATLC TO 69W...WHERE A FEW VERY LONG AND
THIN BROKEN LINES OF CONVECTION CONTINUE TO DEVELOP THIS
EVENING. E OF THIS...A WELL DEFINED 1008 MB LOW WAS CENTERED
NEAR 28N64W. THIS LOW HAS BEEN CLEARLY EVIDENT IN SATELLITE
IMAGERY THE PAST 24 HOURS WITH OCCASIONAL FLARES OF DEEP
CONVECTION ACROSS THE SRN PERIPHERY. HOWEVER THIS SFC LOW WAS
SHIFTING NW AND AWAY FROM THE UPPER CYCLONE OVER THE W CENTRAL
ATLC NEAR 25N61W...AND INTO AN AREA OF WEAKENING UPPER SHEAR
THAT ALLOWED FOR A SIGNIFICANT FLARE OF CONVECTION THIS
AFTERNOON...THIS HAS SINCE DIMINISHED. THIS LOW IS FORECAST TO
BE PULLED BY THE LARGE CIRCULATION OF IRENE TOWARD THE NW AND
WEAKEN THE NEXT 24 HOURS. AN ELONGATED SURFACE TROUGH WAS
LOCATED ABOUT 360 NM TO THE E OF THIS SFC LOW AND HAS BEEN
MOVING IN TANDEM WITH THE LOW FOR THE PAST FEW DAYS. LLVL
CONVERGENCE ON THE E SIDE OF THIS TROUGH WAS PRODUCING SCATTERED
CONVECTION. WEAK HIGH PRES AND LIGHT TO MODERATE ANTICYCLONIC
FLOW PREVAIL ELSEWHERE TO THE E OF THIS TROUGH AND NW OF FORMER
T.D. TEN...IN AN AREA OF BROAD SUBSIDENCE AND FAIR WEATHER. AS
MENTIONED ABOVE IN THE CARIB SECTION...THE ATLC SURFACE RIDGE
WILL BUILD WEST AND SOUTHWESTWARD IN THE WAKE OF IRENE MONDAY
THROUGH WEDNESDAY.

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

$$
STRIPLING




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