[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 151805
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED SEP 15 2010

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...

TROPICAL STORM KARL IS CENTERED NEAR 18.8N 88.7W AT 15/1800 UTC
OR ABOUT 30 NM NE OF CHETUMAL MEXICO OR ABOUT 120 NM ESE OF
CAMPECHE MEXICO MOVING W AT 12 KT. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 994 MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH
GUSTS TO 55 KT. 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. NUMEROUS STRONG CONVECTION IS WITHIN 60 NM OF
THE CENTER IN THE ALL QUADRANTS WITH SCATTERED MODERATE/STRONG
CONVECTION COVERING THE REMAINDER OF THE AREA WITHIN 120 NM OF
THE CENTER IN ALL QUADRANTS. KARL SHOULD WEAKEN TODAY AS THE
CENTER CROSSES THE YUCATAN PENINSULA.  RE-INTENSIFICATION IS
EXPECTED ON THURSDAY OR FRIDAY AFTER THE CENTER EMERGES INTO THE
BAY OF CAMPECHE.

HURRICANE IGOR IS CENTERED NEAR 19.8N 55.0W AT 15/1500 UTC OR
ABOUT 470 NM ENE OF THE NORTHERN LEEWARD ISLANDS AND ABOUT 915
NM KM SE OF BERMUDA MOVING W-NW AT 7 KT. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 942 MB. MAXIMUM SUSTAINED WIND SPEED IS 115
KT WITH GUSTS TO 140 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.
NUMEROUS STRONG CONVECTION IS WITHIN 60 NM FROM THE CENTER IN
THE N SEMICIRCLE AND 120 NM IN THE S SEMICIRCLE.  SCATTERED
MODERATE/ISOLATED STRONG CONVECTION COVERING THE REMAINDER OF
THE AREA WITHIN 120 NM FROM THE CENTER IN THE N SEMICIRCLE AND
180 NM IN THE S SEMICIRCLE.  SOME FLUCTUATIONS IN STRENGTH ARE
POSSIBLE DURING THE NEXT OR TWO...BUT IGOR IS EXPECTED TO REMAIN
A DANGEROUS HURRICANE.

HURRICANE JULIA IS CENTERED NEAR 18.2N 32.7W AT 15/1500 UTC OR
ABOUT 515 NM WNW OF THE CAPE VERDE ISLANDS MOVING NW AT 15 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 950 MB. MAXIMUM SUSTAINED
WIND SPEED IS 115 KT WITH GUSTS TO 140 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
FOR MORE DETAILS. NUMEROUS STRONG CONVECTION IS WITHIN 90 NM
FROM THE CENTER IN THE SW SEMICIRCLE AND 60 NM FROM THE CENTER
IN THE NE SEMICIRCLE.  SCATTERED MODERATE/ ISOLATED STRONG
CONVECTION COVERING THE REMAINDER OF THE AREA WITHIN 120 NM FROM
THE CENTER.  JULIA IS EXPECTED TO MAINTAIN ITS INTENSITY TODAY
BEFORE SLOWLY WEAKENING LATER ON THURSDAY.

...ITCZ...

THE ITCZ...OR PERHAPS BETTER DESCRIBED TODAY AS A MONSOONAL
TROUGH BECAUSE OF THE CONVERGENCE OF NE AND SW SURFACE
WINDS...REMAINS DISCONTINUOUS ACROSS THE ATLANTIC DUE TO
HURRICANES IGOR AND JULIA. THE AXIS OF THE ITCZ EXTENDS FROM
10N14W TO 11N26W AND AGAIN FROM 10N36N TO 11N44W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM N OF THE
AXIS FROM 14W TO 26W.

...DISCUSSION...

GULF OF MEXICO...
AT THE SURFACE...MODERATE RIDGING COVERS THE GULF WITH WEAK E
WINDS PREDOMINATING...EXCEPT FOR NEAR THE YUCATAN CHANNEL.  NEAR
THE LATTER...THE OUTER RAINBANDS FROM TROPICAL STORM KARL ARE
PRODUCING SCATTERED SHOWERS AND THUNDERSTORMS WITH WINDS UP TO
25 KT.  SCATTERED SHOWERS AND THUNDERSTORMS ARE ALSO PREVALENT
OVER AND TO THE WEST OF THE FLORIDA KEYS...PERHAPS ALSO PARTLY
IN ASSOCIATION WITH THE OUTER CIRCULATION OF THE TROPICAL
STORM.  IN THE UPPER LEVELS...A BROAD ANTICYCLONE IS CENTERED
NEAR 28N87W WITH DRY...SUBSIDENT CONDITIONS OBSERVED IN THE
NORTHERN HALF OF THE GULF.  OUTFLOW FROM KARL IS ENHANCING THE
ANTICYCLONE FLOW COVERING THE GULF.

CARIBBEAN SEA...
TROPICAL STORM KARL...WHICH HAS NOW MADE LANDFALL NEAR THE
BELIZE-MEXICO BORDER...IS THE MAIN WEATHER FEATURE OVER THE
CARIBBEAN AND CENTRAL AMERICA.  IN ADDITION TO THE CONVECTIVE
STRUCTURES ASSOCIATED WITH THE CYCLONE NOTED ABOVE...NUMEROUS
MODERATE/ISOLATED STRONG CONVECTION IS OBSERVED IN SOME BANDING
FEATURES FROM KARL SOUTH OF CUBA AND OVER THE EXTREME NW
CARIBBEAN SEA.  AWAY FROM KARL...WINDS ARE QUITE WEAK FROM THE
EAST.  THE ONE EXCEPTION IS FOR SOME OF THE LESSER ANTILLES
WHICH HAVE EITHER CALM WINDS OR WEAKLY N TO W WINDS...DUE TO THE
LARGE WIND FIELD OF HURRICANE IGOR.  IN THE UPPER LEVELS...N TO
NE FLOW IN THE WESTERN AND CENTRAL CARIBBEAN PREVAILS UNDER THE
INFLUENCE OF THE AFOREMENTIONED UPPER RIDGE IN THE NORTHERN
GULF.  IN THE EASTERN CARIBBEAN...A WEAK UPPER TROUGH IS
OBSERVED AND IS ASSOCIATED WITH QUITE DRY SUBSIDENT FLOW.

ATLANTIC OCEAN...
TODAY TWO MAJOR HURRICANES ARE PRESENT SIMULTANEOUSLY IN THE
TROPICAL NORTH ATLANTIC WITH CAT 4 IGOR AND CAT 4 JULIA...QUITE
A RARE EVENT.  AWAY FROM THESE CYCLONES...WINDS ARE RELATIVELY
LIGHT AS THE TYPICAL BERMUDA-AZORES HIGH IS QUITE WEAKENED AND
DISPLACED NORTHEASTWARD COMPARED WITH TYPICAL CONDITIONS.  THE
ONLY MINOR SYNOPTIC FEATURE OF NOTE IS THE TAIL END OF A
STATIONARY FRONTAL BOUNDARY 30N57W TO 32N53W AND NORTHEASTWARD
FROM THERE.  NO DEEP CONVECTION IS FOUND IN ASSOCIATION WITH
THIS BOUNDARY...THOUGH THERE MAY BE SOME LOW-TOPPED SHOWERS
PRESENT WITHIN 30 NM OF THE AXIS.  IN THE UPPER LEVELS...AN
UPPER HIGH IS NEAR 19N48W TO THE EAST OF IGOR.  THIS...ALONG
WITH RIDGING EXTENDING FROM WEST AFRICA ALONG 20N...IS PRODUCING
NORTHEASTERLY FLOW THROUGHOUT THE REGION IN THE UPPER LEVELS.
IT IS OF INTEREST THAT THE VERY LARGE AND STRONG HURRICANE IGOR
IS PRODUCING UPPER LEVEL CYCLONIC FLOW DISCERNIBLE ON THE
SYNOPTIC SCALE BEFORE THIS OUTFLOW TURNS ANTICYCLONIC FARTHER
FROM THE SYSTEM.  ADDITIONALLY...AN UPPER LOW IS DIGGING
SOUTHWARD TO THE NORTHWEST OF HURRICANE JULIA AND IS CURRENTLY
NEAR 20N37W.  WHILE THIS UPPER FEATURE THUS FAR MAY HAVE
ASSISTED THE OUTFLOW OF JULIA...IT IS POSSIBLE THAT THE
SOUTHWESTERLY WINDS ASSOCIATED WITH THE TROUGH MAY BEGIN TO
CAUSE SOME DISRUPTIVE VERTICAL SHEAR IN THE NEXT DAY OR TWO OVER
THE HURRICANE.

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

$$
LANDSEA



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