Tropical Weather Discussion
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000
AXNT20 KNHC 311735
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI JUL 31 2015

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.

...TROPICAL WAVES...

A TROPICAL WAVE EMERGED OFF THE WEST COAST OF AFRICA OVERNIGHT
AS INDICATED BY VERTICAL CROSS SECTION TIME SERIES OVER DAKAR.
THE WAVE NOW EXTENDS FROM 09N20W TO 18N19W...MOVING W AT AN
ESTIMATED 10 TO 15 KT. THIS WAVE IS EMBEDDED IN HIGH MOISTURE S
OF 16 AND COINCIDES WITH A 700 MB INVERTED TROUGH FROM 15W TO
21W. SCATTERED MODERATE CONVECTION IS FROM 11N TO 15N BETWEEN
16W AND 24W.

A CENTRAL ATLC TROPICAL WAVE EXTENDS FROM 09N47W TO 19N49W...
MOVING W AT 15 TO 20 KT OVER THE PAST 24 HOURS. THE WAVE
COINCIDES WITH 700 MB TROUGHING BETWEEN 42W AND 52W. A POLEWARD
SURGE OF MODERATE MOISTURE ACCOMPANIES THE WAVE AXIS. ISOLATED
MODERATE CONVECTION IS FROM 08N TO 11N BETWEEN 43W AND 48W.

A CARIBBEAN TROPICAL WAVE EXTENDS FROM 09N78W TO 19N75W MOVING W
AT 15 TO 20 KT OVER THE PAST 24 HOURS. THE WAVE COINCIDES WITH
BROAD 700 MB TROUGHING BETWEEN 70W-83W. ISOLATED MODERATE
CONVECTION IS S OF 10N BETWEEN 76W AND 79W.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH AXIS EXTENDS FROM THE AFRICAN COAST NEAR
14N17W TO 14N19W...THEN RESUMES W OF THE E ATLC TROPICAL WAVE
NEAR 13N21W TO A 1009 MB LOW NEAR 12N33W TO 08N45W. THE ITCZ
BEGINS NEAR 08N48W AND EXTENDS TO THE S AMERICA COAST NEAR
09N61W. WIDELY SCATTERED MODERATE CONVECTION IS WITHIN 125 NM N
AND 250 NM S OF THE MONSOON TROUGH AND ITCZ AXIS.

...DISCUSSION...

GULF OF MEXICO...
NORTHEASTERLY FLOW ALOFT PREVAILS OVER THE GULF ON THE
SOUTHEASTERN PERIPHERY OF AN UPPER LEVEL ANTICYCLONIC
CIRCULATION CENTERED OVER CENTRAL TEXAS. AN UPPER LEVEL TROUGH
OVER THE EASTERN US SUPPORTS A FRONTAL SYSTEM THAT EXTENDS A
COLD FRONT INTO THE GULF NEAR 30N87W TO 29N91W TO 29N95W. A PRE-
FRONTAL SURFACE TROUGH EXTENDS FROM 30N86W TO 27N93W. CLUSTERS
OF MODERATE TO STRONG CONVECTION ARE FROM 25N TO 29N BETWEEN 87W
AND 97W. NW WINDS OF 10 TO 15 KT ARE N OF THE FRONT. NW WINDS OF
5 TO 10 KT ARE BETWEEN THE FRONT AND NORTHERN GULF SURFACE
TROUGH. A 1016 MB HIGH CENTERED NEAR 23N94W HAS AN AXIS THAT
EXTENDS E TO THE FL STRAITS THEN E TO THE W ATLC. SW WINDS OF 10
TO 15 KT ARE BETWEEN THE HIGH AND THE NORTHERN GULF SURFACE
TROUGH. SE WINDS OF 5 TO 10 KT ARE S OF THE HIGH. A CONVECTION
FREE DIURNAL SURFACE TROUGH IS OVER THE SW GULF FROM 18N94W TO
21N92W. THE COLD FRONT WILL STALL OUT OVER THE N GULF TONIGHT
AND WILL DRIFT SLOWLY BACK NORTH INLAND SATURDAY WHILE THE PRE-
FRONTAL TROUGH REMAINS OVER THE NORTHERN GULF THROUGH SUNDAY.
ONGOING CONVECTION WILL BE LIKELY OVER THE N GULF THROUGH
SUNDAY.

CARIBBEAN SEA...
AN UPPER LOW IS CENTERED OVER THE NW CARIBBEAN NEAR 16N85W WITH
ANOTHER UPPER LOW CENTERED OVER THE SE BAHAMAS. UPPER LEVEL
DIFFLUENCE BETWEEN THESE TWO LOWS SUPPORTS ISOLATED MODERATE
CONVECTION FROM 17N TO 19N BETWEEN 79W AND 85W. ANOTHER AREA OF
UPPER LEVEL DIFFLUENCE IS OVER THE EASTERN CARIBBEAN SUPPORTING
ISOLATED MODERATE CONVECTION FROM 12N TO 18N BETWEEN THE LESSER
ANTILLES AND 67W...INCLUDING SAINT LUCIA. ELSEWHERE...A 1016 MB
HIGH IS CENTERED NEAR 21N84W AND IS AN EXTENSION OF RIDGING OVER
THE ATLC. THE PRESSURE GRADIENT BETWEEN THE RIDGE AND LOWER
PRESSURE OVER S AMERICA SUPPORTS STRONG TRADES OVER THE S
CENTRAL CARIBBEAN S OF 17N. MODERATE TO FRESH TRADE WINDS
DOMINATE MOST OF THE REMAINDER OF THE CARIBBEAN. A TROPICAL WAVE
IS OVER THE WESTERN CARIBBEAN. PLEASE REFER TO THE TROPICAL
WAVES SECTION FOR MORE DETAILS. CONVECTION WILL REMAIN POSSIBLE
OVER THE EASTERN CARIBBEAN IN FAVORABLE UPPER LEVEL DIFFLUENCE
AND WITH DEEP MOISTURE IN PLACE THROUGH SATURDAY. CONVECTION
WILL INCREASE OVER THE SW CARIBBEAN THROUGH TONIGHT AS THE
WESTERN CARIBBEAN TROPICAL WAVE ENTERS A REGION OF FAVORABLE
UPPER LEVEL DIFFLUENCE.

...HISPANIOLA...
A MOIST AIRMASS HAS SPREAD ACROSS THE ISLAND TODAY AND IS
SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER THE
ISLAND THIS AFTERNOON. ISOLATED SHOWERS SHOULD CONTINUE
OVERNIGHT WITH SCATTERED THUNDERSTORMS FORECAST TO OCCUR
SATURDAY AFTERNOON.

ATLANTIC OCEAN...
UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER TROUGH OVER THE EASTERN
US AND UPPER LOW OVER THE SE BAHAMAS SUPPORTS SCATTERED MODERATE
CONVECTION FROM 26N TO 31N BETWEEN 76W AND 81W...INCLUDING THE
NORTHERN BAHAMAS. A FRONTAL SYSTEM MOVING OFFSHORE S
CAROLINA...ASSOCIATED WITH THE E COAST UPPER TROUGH...IS HELPING
TO ENHANCE THE CONVECTION N OF 29N. OTHERWISE...THE SUBTROPICAL
N ATLC IS FREE OF DEEP CONVECTION WITH A PAIR OF WEAK UPPER
LEVEL DISTURBANCES SUPPORTING ISOLATED SHOWERS AND THUNDERSTORMS
FROM 24N TO 28N BETWEEN 52W AND 59W...AND FROM 24N TO 28N
BETWEEN 41W AND 48W. AT THE SURFACE...A 1023 MB HIGH CENTERED
NEAR 29N62W AND A 1025 MB HIGH CENTERED NEAR 31N33W SUPPORT
RIDGING ACROSS MOST OF THE SUBTROPICAL N ATLC. TWO TROPICAL
WAVES ARE OVER THE TROPICAL N ATLC. PLEASE REFER TO THE TROPICAL
WAVES SECTION FOR MORE DETAILS. OVER THE NEXT 24 HOURS
CONVECTION WILL CONTINUE FROM THE N BAHAMAS AND NORTHWARD W OF
75W.

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

$$
LATTO


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