[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 261757
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON AUG 26 2013

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
1715 UTC.

...SPECIAL FEATURES...
TROPICAL DEPRESSION FERNAND IS CENTERED NEAR 20.3N 97.7W AT
26/1500 UTC OR ABOUT 45 NM SSW OF TUXPAN MEXICO MOVING NW AT 8
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB. MAXIMUM
SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. SCATTERED
MODERATE AND ISOLATED STRONG CONVECTION IS FROM 19N-24N BETWEEN
96W-99W...WITH WIDELY SCATTERED MODERATE CONVECTION ELSEWHERE
FROM 17N-26N BETWEEN 92W-100W. THE MOST SIGNIFICANT IMPACT FROM
FERNAND REMAINS THE LARGE AMOUNTS OF RAINFALL EXPECTED OVER A
LARGE PORTION OF EAST-CENTRAL MEXICO DURING THE NEXT 24 TO 48
HOURS. THIS PRECIPITATION IS LIKELY TO CAUSE LIFE-THREATENING
FLASH FLOODS AND MUD SLIDES. SEE LATEST NHC INTERMEDIATE PUBLIC
ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31 KNHC AND THE
FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21
KNHC FOR MORE DETAILS.

...TROPICAL WAVES...
TROPICAL WAVE EXTENDS FROM A 1011 MB LOW CENTERED NEAR 08N23W TO
ANOTHER 1011 MB LOW CENTERED NEAR 17N20W. WHILE THE WAVE AXIS
HAS EMERGED OFF THE WEST AFRICA COAST OVER THE PAST 24 HOURS...
THESE LOW-LEVEL CYCLONIC CIRCULATIONS REPRESENT THE SOUTHERN AND
NORTHERN VORTICITY CENTERS RESPECTIVELY ALONG THE WAVE AXIS. THE
SOUTHERN VORTICITY MAXIMUM CARRIES WITH IT THE MOST CONVECTION
WHICH REMAINS EMBEDDED WITHIN THE MONSOON TROUGH AXIS FROM 09N-
12N BETWEEN 19W-27W. AS THE LOW-LEVEL ENERGY CONTINUES TO
PROPAGATE WESTWARD AS A WHOLE...THE LOW CENTERS ARE EXPECTED TO
ABSORB INTO ONE BROADER CYCLONIC CIRCULATION ALONG THE WAVE AXIS
IN THE VICINITY OF 10N30W. BOTH PRIMARY GLOBAL MODELS...THE GFS
AND ECMWF BOTH SUGGEST THIS SCENARIO OCCURRING OVER THE NEXT 24
HOURS WITH THE SOUTHERN VORTICITY MAXIMUM CONTINUING WESTWARD AS
THE DOMINATE FEATURE WITH THE TROPICAL WAVE ACROSS THE EASTERN
TROPICAL ATLC.

TROPICAL WAVE EXTENDS FROM 14N41W TO 24N38W MOVING W AT 10-15
KT. THE WAVE REMAINS EMBEDDED WITHIN A MAXIMUM OF TOTAL
PRECIPITABLE WATER EXTENDING NORTHWARD FROM THE MONSOON TROUGH
REGION FROM 13N-24N BETWEEN 33W-41W AND COINCIDES WITH A 700 MB
TROUGH AXIS WITH A RELATIVE VORTICITY MAXIMUM CENTERED IN THE
VICINITY OF THE NORTHERN EXTENT OF THE WAVE AXIS NEAR 22N39W.
THE WAVE LACKS ANY SIGNIFICANT DEEP CONVECTION AT THIS TIME DUE
TO THE PRESENSE OF THE SAHARAN AIR LAYER ACROSS MUCH OF THE
CENTRAL AND EASTERN ATLC.

TROPICAL WAVE EXTENDS FROM 11N77W TO 20N74W MOVING W AT 15 KT.
THE WAVE CONTINUES TO BE EMBEDDED WITHIN BROAD LOW-LEVEL
TROUGHING ACROSS THE CENTRAL AND WESTERN CARIBBEAN SEA AS
STRONGER EASTERLY TRADES ARE NOTED TO THE EAST OF THE WAVE AXIS
BETWEEN 68W-78W. TOTAL PRECIPITABLE WATER IMAGERY INDICATES THE
WAVE LIES WITHIN A RELATIVELY MOIST ENVIRONMENT WITH SCATTERED
MODERATE CONVECTION OCCURRING FROM 12N-17N BETWEEN 75W-84W.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM 12N20W TO 08N25W TO 13N33W TO
11N42W TO A 1012 MB LOW NEAR 10N52W TO 08N57W. SCATTERED
MODERATE CONVECTION IS FROM 09N-13N BETWEEN 19W-28W...FROM 05N-
08N BETWEEN 27W-30W...AND FROM 08N-13N BETWEEN 35W-58W.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY INDICATES AN UPPER LEVEL TROUGH AXIS EXTENDS
FROM OVER THE SW NORTH ATLC NEAR 29N77W TO OVER THE CENTRAL
FLORIDA PENINSULA TO OVER PORTIONS OF THE NE GULF NEAR 28N85W.
THIS TROUGHING ALOFT SUPPORTS A STATIONARY FRONT DRAPED ACROSS
THE NORTHERN GULF WATERS ALONG 29N FROM THE BIG BEND OF FLORIDA
TO THE MISSISSIPPI RIVER DELTA REGION AND ALONG THE TEXAS AND
LOUISIANA COAST. E OF 90W...MOST OF THE MIDDLE TO UPPER LEVEL
DYNAMICS ARE WELL SOUTH OF THE FRONT WITH THE UPPER LEVEL TROUGH
GENERATING WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS FROM 23N-
26N BETWEEN 80W-83W...AND FROM 24N-28N BETWEEN 83W-88W. W OF
90W...LOW-LEVEL MOISTURE CONVERGENCE ALONG AND SOUTH OF THE
FRONT IS GENERATING SCATTERED SHOWERS AND TSTMS N OF 27N W OF
92W. SLIGHTLY FARTHER SOUTH...AN UPPER LEVEL ANTICYCLONIC
CIRCULATION IS CENTERED IN THE WESTERN GULF NEAR 25N97W AND
CONTINUES TO PROVIDE A DIFFLUENT ENVIRONMENT ALOFT FOR
CONVECTION ASSOCIATED WITH TROPICAL DEPRESSION FERNAND AS IT
CONTINUES TO WEAKEN OVER INLAND EAST-CENTRAL MEXICO THIS
AFTERNOON. SCATTERED SHOWERS AND TSTMS ARE OCCURRING FROM 17N-
26N BETWEEN 92W-100W. FURTHER ENHANCING THIS CONVECTION IS WEAK
SURFACE TROUGHING PARALLELING THE SE TEXAS AND EASTERN MEXICO
COAST FROM TUXPAN NORTHWARD TO MATAGORDA BAY. WITH A SURFACE
RIDGE ANCHORED TO THE NORTH OVER THE SE CONUS...E-SE WINDS ARE
FORECAST TO PERSIST THROUGH LATE WEDNESDAY WHEN THE SURFACE
RIDGING WILL SLOWLY SHIFT SOUTHWARD INTO THE GULF BY LATE
THURSDAY INTO FRIDAY.

CARIBBEAN SEA...
UPPER LEVEL NORTHEASTERLY FLOW IS OVER MUCH OF THE NW CARIBBEAN
AND CENTRAL AMERICA BETWEEN AN ANTICYCLONE CENTERED OVER THE NW
GULF OF MEXICO NEAR 25N97W AND AN UPPER LEVEL LOW CENTERED OVER
THE SW CARIBBEAN NEAR 10N81W. WATER VAPOR IMAGERY INDICATES MUCH
OF THE NW CARIBBEAN REMAINS DRY AND STABLE ALOFT WITH GENERALLY
CLEAR SKIES THIS AFTERNOON. HOWEVER...AS FLOW ALOFT TRANSITIONS
TO CYCLONIC ALONG A TROUGH AXIS EXTENDING FROM THE UPPER LEVEL
LOW TO OVER JAMAICA NEAR 18N78W...MOISTURE AND CONVECTION
INCREASE ACROSS THE CENTRAL AND SW CARIBBEAN IN THE VICINITY OF
A TROPICAL WAVE ALONG 76W. SCATTERED SHOWERS AND TSTMS ARE
CONCENTRATED WEST OF THE WAVE AXIS FROM 12N-16N BETWEEN 79W-84W
WITH ISOLATED SHOWERS AND TSTMS OCCURRING ELSEWHERE FROM 09N-18N
BETWEEN 68W-85W. A PORTION OF THIS CONVECTION REMAINS FOCUSED
ALONG THE MONSOON TROUGH AXIS ANALYZED ALONG 10N FROM NORTHERN
COLOMBIA WESTWARD ACROSS COSTA RICA AND INTO THE EAST PACIFIC
REGION. FINALLY...MOIST SOUTHERN FLOW ALOFT DOMINATES ACROSS THE
EASTERN CARIBBEAN BETWEEN THE AFOREMENTIONED TROUGH AXIS AND AN
UPPER LEVEL ANTICYCLONE CENTERED OVER THE SW NORTH ATLC NEAR
19N63W. WHILE NO SIGNIFICANT DEEP CONVECTION IS OCCURRING EAST
OF THE TROPICAL WAVE...A SURFACE TROUGH...MOST LIKELY RESIDUAL
ENERGY LEFT BEHIND BY THE TROPICAL WAVE...IS ANALYZED FROM
15N65W TO 22N63W AND CONTINUES TO GENERATE WIDELY SCATTERED LOW-
TOPPED SHOWERS AND TSTMS N OF 13N BETWEEN 60W-72W.

HISPANIOLA...
MOIST SOUTHWESTERLY FLOW ALOFT IS OVER HISPANIOLA THIS AFTERNOON
AND IS PROVIDING FOR AN OVERALL DIFFLUENT ATMOSPHERE FOR THE
ISLAND. MOVING WESTWARD BENEATH THIS FLOW IS SURFACE TROUGH
ANALYZED FROM 15N65W TO 22N63W. LOW-LEVEL MOISTURE IS FOCUSED ON
BOTH SIDES OF THE SURFACE TROUGH BETWEEN 60W-70W WHICH IS
ALREADY PROVIDING THE ISLAND WITH ISOLATED SHOWERS E OF 71W.
MOISTURE AND PRECIPTATION IS EXPECTED TO INCREASE AS THE SURFACE
TROUGH MOVES WEST OVER THE NEXT 24 TO 48 HOURS. PEAK DAYTIME
HEATING AND INSTABILITY WILL LIKELY GENERATE MORE INTENSE
SHOWERS AND TSTMS WITH ANY ACTIVITY DIMINISHING BEYOND THE LATE
EVENING HOURS.

ATLANTIC OCEAN...
A MIDDLE TO UPPER LEVEL TROUGH AXIS EXTENDS INTO THE DISCUSSION
AREA NEAR 32N68W IN THE SW NORTH ATLC AND CONTINUES
SOUTHWESTWARD TO A BASE OVER THE CENTRAL FLORIDA PENINSULA NEAR
27N81W. THIS TROUGHING ALOFT SUPPORTS A STATIONARY FRONT
ANALYZED FROM 32N65W TO 30N73W TO THE FLORIDA PENINSULA NEAR
29N81W. WATER VAPOR IMAGERY INDICATES THAT THE UPPER LEVEL
DYNAMICS ARE MORE CONCENTRATED FARTHER SOUTH OVER THE FLORIDA
STRAITS AND ARE GENERATING SCATTERED SHOWERS AND TSTMS FROM 23N-
27N BETWEEN 75W-83W. TO THE NORTHEAST CLOSER TO THE STATIONARY
FRONT...LOW-LEVEL MOISTURE CONVERGENCE ALONG AND SOUTH OF THE
BOUNDARY CONTINUES TO PRODUCE ISOLATED SHOWERS AND TSTMS WITHIN
240 NM SOUTHEAST OF THE FRONT E OF 75W. A PRE-FRONTAL SURFACE
TROUGH FROM 34N60W TO 26N70W IS ALSO PROVIDING FOCUS FOR THE
ONGOING CONVECTION. TO THE SOUTHEAST...A SURFACE TROUGH EXTENDS
FROM THE NE CARIBBEAN SEA NEAR 15N65W TO 22N63W WITH LOW-LEVEL
MOISTURE CONVERGENCE AND INSTABILITY GENERATING WIDELY SCATTERED
LOW-TOPPED SHOWERS FROM 15N-23N BETWEEN 60W-70W. ASIDE FROM THE
TROPICAL WAVE ALONG 40W...THE REMAINDER OF THE CENTRAL AND
EASTERN ATLC IS UNDER THE INFLUENCE OF A SURFACE RIDGE ANCHORED
BY A 1029 MB HIGH CENTERED NORTH OF THE AZORES NEAR 44N25W.

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

$$
HUFFMAN


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