Area Forecast Discussion
Issued by NWS San Juan, PR

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000
FXCA62 TJSJ 231513
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1113 AM AST SAT AUG 23 2014

.UPDATE...
DOPPLER WEATHER RADAR DETECTED INCREASING SHOWERS AND
THUNDERSTORMS ACROSS THE REGION THIS MORNING. THIS ACTIVITY IS
ASSOCIATED WITH THE TRAILING MOISTURE LEFT BEHIND THE STRONG
TROPICAL WAVE/LOW PRESSURE TO THE NORTH OF HISPANIOLA THIS MORNING.
A MOIST AND UNSTABLE SOUTH SOUTHEAST LOW LEVEL WIND FLOW WILL
CONTINUE TO TRANSPORT ABUNDANT MOISTURE ACROSS PUERTO RICO THIS
AFTERNOON. THIS MOISTURE IN COMBINATION WITH DAYTIME HEATING AND
LOCAL OROGRAPHIC EFFECTS ARE EXPECTED TO INDUCE THE DEVELOPMENT OF
NUMEROUS SHOWERS AND ISOLATED TO SCATTERED THUNDERSTORMS ACROSS
PUERTO RICO. SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DIMINISH
TONIGHT. A DRYING TREND WILL START ON MONDAY...WITH THE RETURN TO
THE TYPICAL SUMMER AFTERNOON SHOWERS AND THUNDERSTORMS OVER WESTERN
AND INTERIOR PUERTO RICO.

&&

.AVIATION...NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS EXPECTED
THIS AFTERNOON MOSTLY ACROSS PUERTO RICO TERMINALS. PERIODS OF
MVFR/IFR CIGS AND VSBYS EXPECTED AT TJPS...TJSJ...TJMZ...TJBQ AND
USVI TERMINALS. AREAL COVERAGE AND INTENSITY OF SHOWERS SHOULD BEGIN
TO DECREASE TONIGHT BUT THICK CLOUD COVER WILL PERSIST THROUGH
SUNDAY MORNING BUT WITH VFR CIGS.

&&

.MARINE...NUMEROUS SHOWERS AND THUNDERSTORMS EXPECTED THIS AFTERNOON
ACROSS THE REGIONAL WATERS. HEAVY RAINS...FREQUENT LIGHTNING AND
GUSTY WINDS TO 30 KT MAY ACCOMPANY THE HEAVIEST SHOWERS.

&&

.PREV DISCUSSION... /ISSUED 335 AM AST SAT AUG 23 2014/

SYNOPSIS...LONG FETCH SERLY FLOW WILL PERSIST THROUGH TUE. TRADE
WINDS WILL RETURN TO THE LOCAL AREA TUESDAY NIGHT. NEXT TROPICAL
WAVE EXPECTED THURSDAY.

DISCUSSION...A VERY MOIST SOUTHEAST FLOW WILL PERSIST THROUGH
SUNDAY WITH A DRYING TREND COMMENCING ON MONDAY. MODELS MAINTAIN
VERY HIGH H85 THETA-E AIR OVR PR TODAY WITH STRONG SFC CONVERGENCE
OVER THE SAME AREAS THAT RECEIVED THE HEAVIEST RAINS YESTERDAY.
FOR THIS REASON WILL EXTEND FLOOD WATCH THROUGH 21Z TODAY. ALTHOUGH
VERY MOIST AIR LINGERS THROUGH SUNDAY...,LOW-MID LEVEL FORCING
DIMINISHES SIGNIFICANTLY TONIGHT AND SUNDAY WHICH SHOULD RESULT
IN A SIG DECREASE IN AREAL COVERAGE AND INTENSITY OF SHOWERS AND
T-STORMS. ANY HEAVY RAINS TONIGHT OR SUNDAY SHOULD BE LOCALIZED
AND DOES NOT JUSTIFY EXTENDING THE FLOOD WATCH ANY FURTHER THAN
21Z.

UPPER LEVEL RIDGE NORTH OF THE AREA WILL THEN STEER A TUTT LOW
ACROSS THE ERN CARIB SUN NIGHT AND MON WITH SHARP DRY AIR
ADVECTION FROM THE EAST. TRADE WINDS STRENGTHEN TUE NIGHT THROUGH
THU AS STRONG BERMUDA-AZORES HIGH REESTABLISHES NORTH OF THE AREA.
THE 00Z ECMWF SHOWS A ROBUST TROPICAL WAVE WITH A LOT OF LOW-LEVEL
CURVATURE MOVING THRU THE ERN CARIB THU WHILE THE GFS IS MORE
FLAT AND SUPPRESSED WITH THIS WAVE. ONLY ONE 23/00Z GEFS MEMBER
OUT OF 20 SHOWS TC DEVELOPMENT WITH THIS WAVE WHILE NONE OF THE
22/12Z ECWMF MEMBERS SHOWS DEVELOPMENT.

AVIATION...NMRS SHOWERS AND SCT T-STORMS EXPECTED TODAY WITH
MVFR/IFR CIGS AND VSBYS AT JPS...JSJ AND USVI TERMINALS. AREAL
COVERAGE AND INTENSITY OF SHOWERS SHOULD BEGIN TO DECREASE TONIGHT
BUT THICK CLOUD COVER WILL PERSIST THROUGH SUN BUT WITH VFR CIGS.

MARINE...NMRS SHOWERS AND T-STORMS TODAY ALL WATERS XCPT ANEGADA
PASSAGE. HEAVY RAINS...FREQ LIGHTNING AND GUSTY WINDS TO 30 KT MAY
ACCOMPANY THE HEAVIEST SHOWERS.

HYDROLOGY...RISK OF FLOODING WILL CONTINUE THROUGH 21Z TODAY AS
BANDS OF +SHRA MOVE REPEATEDLY OVER THE SAME AREAS THAT RECEIVED
QUITE A BIT OF RAIN YESTERDAY. SRN COAST AND THE ERN HALF OF PR
WILL BE AT GREATEST RISK OF FLOODING WITH NORTHWEST PR HAVING THE
LEAST RISK. ADDITIONAL LOCALIZED RAINFALL AMOUNTS OF 2 TO 5 INCHES
WILL BE POSSIBLE WITH THE HEAVIEST SHOWERS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  77  87  78 /  70  30  30  30
STT  85  78  88  79 /  70  40  20  20

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...FLASH FLOOD WATCH UNTIL 5 PM AST THIS AFTERNOON FOR CENTRAL
     INTERIOR-CULEBRA-EASTERN INTERIOR-MAYAGUEZ AND VICINITY-
     NORTH CENTRAL-NORTHEAST-NORTHWEST-PONCE AND VICINITY-SAN
     JUAN AND VICINITY-SOUTHEAST-SOUTHWEST-VIEQUES-WESTERN
     INTERIOR.

VI...FLASH FLOOD WATCH UNTIL 5 PM AST THIS AFTERNOON FOR ST CROIX-ST.
     THOMAS/ST. JOHN/ADJACENT ISLANDS.

COASTAL WATERS...
     SMALL CRAFT ADVISORY UNTIL 6 PM AST THIS EVENING FOR ATLC WATERS
     OF PUERTO RICO AND USVI FROM 10NM TO 19.5N.

&&

$$

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