Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 221429
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1029 AM AST FRI AUG 22 2014

.UPDATE...LATEST VISIBLE IMAGES AND DOPPLER RADAR INDICATED AN
AREA OF SHOWERS AND THUNDERSTORMS DEVELOPING OVER THE COASTAL
WATERS OF SOUTHEASTERN PUERTO RICO. A LINE OF HEAVY SHOWERS WITH
THUNDERSTORMS BEGAN TO MOVE INLAND OVER THE SOUTHEAST SECTION OF
PUERTO RICO. URBAN AND SMALL STREAM FLOODING ARE LIKELY TO
OCCUR...AS THIS ACTIVITY INTENSIFIED OVER THAT AREA. ACTIVE
AFTERNOON IS IN STORE FOR PUERTO RICO AND THE U.S. VIRGIN ISLANDS
AS DEEP TROPICAL MOISTURE COMBINE WITH DAYTIME HEATING. REFER TO
LATEST LOCAL FLOOD PRODUCTS FROM THE NATIONAL WEATHER SERVICE IN
SAN JUAN.

&&

.AVIATION...NO CHANGES TO PREVIOUS DISCUSSION AS...VERY ACTIVE PERIOD
IS EXPECTED TO CONTINUE THIS AFTERNOON WITH TSRA THROUGH THE AREA AND LOW
CIGS. WINDS WILL BE FROM THE E-NE...GRADUALLY CHANGING TO
SOUTHEAST THROUGH THE DAY AND GUSTING UP TO 30 KNOTS...ESPECIALLY
NEAR TSRA AS THE LOW PRESSURE PASSES. ALSO...CIGS BELOW FL020 AND
HEAVY RAIN SHALL BE EXPECTED WITH THIS ACTIVITY. PREVAILING MVFR
CONDS ARE EXPECTED WITH PERIODS OF IFR CONDS LIKELY AT TIMES
ACROSS THE LOCAL TERMINALS

&&

.MARINE...SHOWERS AND THUNDERSTORMS WILL MAINTAIN HAZARDOUS MARINE
CONDITIONS THROUGHOUT THE DAY. NO CHANGES TO PREVIOUS DISCUSSION.


&&

.PREV DISCUSSION... /ISSUED 558 AM AST FRI AUG 22 2014/

SYNOPSIS...UPPER LEVEL RIDGE WILL HOLD THROUGH THE WEEKEND AND
THEN WEAKEN THROUGH THE END OF NEXT WEEK. LOW PRES EXPECTED TO
PASS SOUTH OF PR TODAY AND MOVE INTO THE DOMINICAN REPUBLIC SATURDAY.

DISCUSSION...SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH LOW
PRES SOUTH OF ST. CROIX REMAIN DISORGANIZED. AN ASCAT PASS AT
0157Z DID NOT LONGER SHOW WINDS OF 35 KT AND LATEST INITIALIZATION
FROM NHC HAS DROPPED WINDS TO 30 KT. SO IT IS BECOMING QUITE LIKELY
THAT TROPICAL STORM WARNINGS WILL NOT BE NEEDED FOR THIS EVENT.
HOWEVER...AS WE ALL KNOW HEAVY RAINFALL IS NOT DIRECTLY RELATED
WITH THE INTENSITY OF A TROPICAL CYCLONE. LATEST BLENDED TPW
PRODUCT SHOWS A VERY DEEP MOISTURE PLUME PRESENT OVR THE ERN
CARIBBEAN WITH PWAT VALUES EXCEEDING 2.5 INCHES OR AT THE 99TH
PERCENTILE USING A PWAT CLIMO SINCE 1950. AS LOW PRES MOVES SOUTH
OF PR AND WINDS SHIFT TO THE SOUTHEAST AROUND 15Z EXPECT VERY
INTENSE RAINFALL TO MOVE OVR PR. PERIOD OF MOST INTENSE RAINFALL
IS EXPECTED FROM ABOUT 11 AM TO 5 PM TODAY WITH THE HEAVIEST
ACCUMULATIONS OVER SRN PR AND THE ERN THIRD OF PR WHERE BEST
TOPOGRAPHICAL FORCING IS EXPECTED. IN THESE AREAS RAINFALL TOTALS
COULD EXCEED 10 INCHES. AFTER 00Z SAT...BEST FORCING WILL SHIFT
INTO THE MONA PASSAGE AND THE DOMINICAN REPUBLIC WITH RAINFALL
INTENSITY EXPECTED TO DIMINISH SOMEWHAT BUT RAINS WILL CONTINUE
OFF AND ON THROUGH THE NIGHT ON THE SOUTH COAST. AFTER 12Z
SAT...LOW PRES EXPECTED TO MOVE INTO THE ATLC NORTH OF HISPANIOLA
WITH BOTH MOISTURE AND SFC CONVERGENCE DIMINISHING RAPIDLY THROUGH
THE DAY. EXPECT CONDITIONS TO IMROVE RAPIDLY THROUGH THE DAY BUT
IT WILL STILL REMAIN CLOUDY WITH A RISK OF SOME SHOWERS. MUCH
DRIER WX EXPECTED FOR NEXT WEEK.

AVIATION...VERY ACTIVE PERIOD IS EXPECTED TODAY WITH TSRA THROUGH
THE AREA AND LOW CIGS. WINDS WILL BE FROM THE E-NE...GRADUALLY
CHANGING TO SOUTHEAST THROUGH THE DAY AND GUSTING UP TO 30
KNOTS...ESPECIALLY NEAR TSRA AS THE LOW PRESSURE PASSES.
ALSO...CIGS BELOW FL020 AND HEAVY RAIN SHALL BE EXPECTED WITH THIS
ACTIVITY. PREVAILING MVFR CONDS ARE EXPECTED WITH PERIODS OF IFR
CONDS LIKELY AT TIMES ACROSS THE LOCAL TERMINALS.

MARINE...WINDS 20-25 KT AND SEAS 7-9 FT ESPECIALLY OVER ATLC
WATERS WHERE PRES GRADIENT IS TIGHTEST. WINDS AND WAVES HIGHER
NEAR THUNDERSTORMS.

HYDROLOGY...TODAY`S EXPECTED HEAVY RAINFALL EVENT APPEARS TO BE
A LONGER DURATION EVENT THAN DURING TS BERTHA AND MOISTURE PLUME
IS ALSO DEEPER WITH THE FOCUS OF HEAVIEST RAINFALL THIS TIME
AROUND OVER ERN THIRD AND SRN PR WHERE RIVERS TEND TO RESPOND A
LOT QUICKER. ALSO...SOIL MOISTURE IS SIGNIFICANTLY HIGHER THIS
TIME AROUND THAN DURING BERTHA MEANING THAT GROUND WILL BE ABLE TO
ABSORB LESS WATER AND MORE WATER WILL TURN INTO RUNOFF WHICH
INCREASES THE RISK FOR MORE FLOODING. RELUCTANT TO GO ANY HIGHER
IN RAINFALL AMOUNTS THAN WHAT WE ALREADY HAVE IN THE FCST DUE TO
THE LACK OF ORGANIZATION OF THE SYSTEM BUT BELIEVE RAINFALL TOTALS
FOR SRN AND ERN PR WILL BE CLOSER TO 10 INCHES WHEN THE RAIN IS
DONE SAT MORNING.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  85  80  85  77 / 100  80  80  30
STT  82  81  82  79 / 100  80  80  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...FLASH FLOOD WATCH THROUGH SATURDAY MORNING 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 THROUGH SATURDAY MORNING FOR ST CROIX-ST.
     THOMAS/ST. JOHN/ADJACENT ISLANDS.

COASTAL WATERS...
     SMALL CRAFT ADVISORY UNTIL 4 PM AST THIS AFTERNOON FOR COASTAL
     WATERS OF NORTHWESTERN PUERTO RICO OUT 10 NM-COASTAL WATERS
     OF SOUTHERN PUERTO RICO OUT 10 NM.

     SMALL CRAFT ADVISORY UNTIL 3 PM AST SATURDAY FOR ANEGADA PASSAGE
     SOUTHWARD TO 17N-ATLC WATERS OF PUERTO RICO AND USVI FROM
     10NM TO 19.5N-CARIBBEAN WATERS OF PUERTO RICO FROM 10 NM TO
     17N-MONA PASSAGE SOUTHWARD TO 17N.

     SMALL CRAFT ADVISORY UNTIL 9 PM AST THIS EVENING FOR COASTAL
     WATERS OF NORTHERN PUERTO RICO OUT 10 NM.

     SMALL CRAFT ADVISORY UNTIL 9 AM AST SATURDAY FOR COASTAL WATERS
     OF NORTHERN USVI AND CULEBRA OUT 10 NM-COASTAL WATERS OF
     SOUTHERN USVI VIEQUES AND EASTERN PUERTO RICO OUT 10 NM.

&&

$$

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