Area Forecast Discussion
Issued by NWS San Juan, PR

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000
FXCA62 TJSJ 260210
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1010 PM AST SUN JAN 25 2015

.UPDATE...ONLY ISOLATED SHOWERS WERE DETECTED THIS EVENING ACROSS
THE SURROUNDING COASTAL WATERS. NO SIGNIFICANT PRECIPITATION WAS
DETECTED OVER LAND AREAS AS THE REGION CONTINUED UNDER THE INFLUENCE
OF A MID TO UPPER LEVEL RIDGE. THIS RIDGE WILL REMAIN AS THE MAIN
WEATHER FEATURE OVER THE REGION UNTIL AT LEAST MONDAY. SUBSIDENCE
ASSOCIATED WITH THE RIDGE WILL MAINTAIN VERY DRY CONDITIONS AT MID
TO UPPER LEVELS...RESULTING IN AN UNFAVORABLE ENVIRONMENT FOR
DEVELOPMENT OF STRONG SHOWERS AND THUNDERSTORMS. THE RIDGE WILL
ERODE BY LATE TUESDAY AS A FRONTAL BOUNDARY APPROACHES TO THE
REGION. THE FRONTAL BOUNDARY WILL BRING AN INCREASE IN CLOUDINESS
AND SHOWERS OVER THE LOCAL ISLANDS LATE TUESDAY AND THEREAFTER.

&&

.AVIATION...MOSTLY VFR CONDS EXPECTED AT ALL TAF SITES OVERNIGHT
WITH BRIEF SHOWERS POSSIBLE IN AND AROUND ISX/JSJ. BRIEF MVFR CONDS
WILL REMAIN POSSIBLE BETWEEN 26/17Z AND 26/20Z AT JMZ/JBQ IN SHRA.
LIGHT WINDS EXPECTED OVERNIGHT...BECOMING ESE AT 10 TO 15 KNOTS WITH
SOME SEA BREEZE VARIATIONS AFT 26/15Z.

&&

.MARINE...TRANQUIL SEAS EXPECTED WILL CONTINUE OVERNIGHT...SEAS MOSTLY
3-5 FT AND WINDS 17 KNOTS OR LESS.

&&

.PREV DISCUSSION... /ISSUED 251 PM AST SUN JAN 25 2015/

SYNOPSIS...
MID TO UPPER LEVEL RIDGE ALOFT WILL REMAIN IN PLACE OVER THE AREA
THROUGH MONDAY...THEN GRADUALLY BEGIN TO ERODE ON EARLY TUESDAY AS
A POLAR TROUGH DEEPENS AND MOVES EASTWARDS ACROSS THE WESTERN
ATLANTIC THROUGH THE END OF THE WORK WEEK. EAST SOUTHEAST LOW
LEVEL WINDS WILL PREVAIL THROUGH A LEAST MONDAY... BECOMING MORE
SOUTHEAST ON TUESDAY AND WEDNESDAY AS A FRONTAL SHEAR LINE SINKS
SOUTHWARDS ACROSS THE SOUTHWEST ATLANTIC TO JUST NORTH AND WEST OF
THE REGION. THIS WILL BE SUPPORTED BY AN INDUCED SURFACE TROUGH
WHICH WILL SET UP ACROSS THE REGION BY THURSDAY AND FRIDAY.

DISCUSSION...
MOSTLY SUNNY SKIES AND LIMITED SHOWER ACTIVITY WAS OBSERVED ACROSS
MOST OF THE ISLANDS TODAY. FEW SHOWERS DEVELOPED ACROSS THE WEST
AND NORTHWEST SECTIONS OF PUERTO RICO AND PRODUCED MOSTLY LIGHT TO
MODERATE DOWNPOURS OF SHORT DURATION. ELSEWHERE MOSTLY FAIR WEATHER
SKIES PREVAILED. HIGH PRESSURE AT ALL LEVELS OF THE ATMOSPHERE WILL
CONTINUE TO DOMINATE THE LOCAL WEATHER PATTERN TO MAINTAIN AN OVERALL
SUBSIDENCE PATTERN ALOFT. THIS IN TURN WILL LIMIT AND SUPPRESS LOCALIZED
CONVECTION.

EVEN DRIER CONDITIONS EXPECTED ON MONDAY WITH ONLY LIMITED PASSING
EARLY MORNING SHOWERS ALONG THE EAST COASTAL AREAS AND OVER THE COASTAL
WATERS. THIS WILL BE FOLLOWED BY ISOLATED TO SCATTERED DIURNALLY INDUCED
CONVECTION MAINLY ACROSS THE WEST CENTRAL AND NORTHWEST INTERIOR SECTIONS
OF PUERTO RICO. MOSTLY SUNNY AND FAIR WEATHER SKIES WILL PERSIST ACROSS
THE REST OF THE ADJACENT ISLANDS INCLUDING THE U.S VIRGIN ISLANDS.

BY TUESDAY...A SURGE OF TRADE WIND MOISTURE IS FORECAST TO MOVE ACROSS
THE EASTERN CARIBBEAN...AS WELL AS THE PREVIOUSLY MENTIONED SHEAR
LINE FORECAST TO APPROACH THE REGION FROM THE SOUTHWESTERN ATLANTIC.
LATEST MODEL GUIDANCE CONTINUED TO SUGGEST INCREASING PWAT VALUES
TO AROUND 1.9 INCHES OR SO BY LATE TUESDAY. THIS ALONG WILL THE
EROSION OF THE UPPER RIDGE WILL ALLOW FOR BETTER CHANCE OF ENHANCED
CONVECTIVE DEVELOPMENT...ESPECIALLY DURING THE AFTERNOON. IMPROVING
WEATHER CONDITIONS SO FAR EXPECTED ON WEDNESDAY.

ON THURSDAY AND FRIDAY ...INCREASING LOW LEVEL CONVERGENCE AND THE
DEPLETION OF THE UPPER RIDGE ALONG WITH A JET SEGMENT MOVING ACROSS
THE REGION WILL CREATE UNSTABLE CONDITIONS AND THEREFORE INCREASE
THE CHANCE FOR ENHANCED CONVECTION WITH POSSIBLE THUNDERSTORM DEVELOPMENT
IN SOME AREAS DURING THAT TIME. WILL CONTINUE TO MONITOR AND SEE HOW
THIS UNFOLDS IN THE LONG TERM.

AVIATION...FEW -SHRA/SHRA ACROSS W INTERIOR PR AND VCTY TJMZ AND
TJSJ TIL 25/22Z. VFR CONDS AT ALL TAF SITES DURG PRD. SCT-BKN
FL025-FL060...BTW PR AND NRN LEEWARDS...CLR ABV...FEW TCU TOPS
160 MAINLY INLAND PR AND OVR COASTAL WATERS. NO SIG OPERATIONAL WX
IMPACTS ATTM. WND 5-15 KTS FM E BLO FL200...BCM FM N-NW AND INCR
W/HT ABV WITH MAX WND FM NW A 65 KTS FL400.

MARINE...
MARINE...TRANQUIL SEAS EXPECTED WILL CONTINUE OVERNIGHT...SEAS MOSTLY
2-4 FT AND WINDS 17 KNOTS OR LESS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  88  74  87 /  30  20  10  40
STT  73  84  75  83 /  40  20  20  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...NONE.
&&

$$

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