Flash Flood Warning 30, NWS JSJ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
406 PM AST THU APR 21 2005

.DISCUSSION...

...SIGNIFICANT WEATHER EVENT SHAPING UP ACROSS PUERTO
RICO...CULEBRA...VIEQUES AND ALL THE VIRGIN ISLANDS...

FORECAST...THE GOOD...THE BAD AND THE REALLY UGLY.

THE GOOD...FOR THE MOST PART SHOWERS AND THUNDERSTORMS WILL DIMINISH
THIS EVENING ACROSS THE NORTHERN COAST OF PUERTO RICO...EXCEPT FOR
ISOLATED TO SCATTERED SHOWERS ACROSS THE SOUTH-SOUTHEAST-EAST
COASTAL WATERS....A FEW WHICH WILL MOVE ON SHORE.

THE BAD...LOCAL AREA SHOULD SEE ABOUT THE SAME WEATHER AS WAS SEEN
THIS AFTERNOON WITH SCATTERED TO NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORM DEVELOPING MAINLY ACROSS THE NORTHERN HALF OF PUERTO
RICO THEN MOVING NORTHWARD INTO THE ATLANTIC.

THE REALLY UGLY...AS WE HAVE BEEN FORECASTING THE PAST SEVERAL DAYS
A STRONG MID/UPPER TROUGH WILL START TO AFFECT THE LOCAL AREA FRIDAY
EVENING THROUGH SUNDAY. WE HAVE THE DYNAMICS FOR A MAJOR FLOOD EVENT
ACROSS PORTIONS OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS. WITH A
SURGE OF DEEP ITCZ MOISTURE EXPECTED TO MOVE NORTHWARD ACROSS THE
LOCAL AREA...HIGH OMEGA VALUES...VERY GOOD DIFFLUENCE ALOFT AND
BEING IN THE RIGHT REAR QUADRANT OF THE JET...AND THIS ALL IN THE
MID/UPPER LEVELS. TO AGGRAVATE THE SITUATION AT LOW LEVELS A
SOUTHERLY LOW LEVEL JET OF 15 TO 20 KNOTS IS EXPECTED TO COME UP
FROM THE SOUTH WHICH WILL TRIGGER GOOD LOW LEVEL CONVERGENCE ACROSS
SOUTHERN FACING COAST WHICH WILL PROPAGATE NORTH TO THE NORTHERN
COASTS AS WELL. BASED ON THE PAST 2 RUNS OF THE GFS...THE MAX LOW
LEVEL CONVERGENCE APPEARS TO OCCUR ACROSS THE EASTERN SECTION OF
PUERTO RICO...OVER CULEBRA...VIEQUES AND THE USVI...ESPECIALLY THE
NORTHERN USVI LATE FRIDAY NIGHT THROUGH SUNDAY. HOWEVER...THE POOL
OF MOISTURE THAT WILL BE ADVECTED FROM THE SOUTH WILL LIKELY BE
ENOUGH FOR WIDESPREAD SHOWERS AREA WIDE.

THIS IS A DANGEROUS SITUATION THE BULK OF THE EVENT IS FORECAST
TO BEGIN DURING THE EVENING OR NIGHT HOURS...YOU ARE URGED TO KEEP
ABREAST OF THIS DEVELOPING WEATHER PATTERN.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  85  76  84 /  20  50  70  70
STT  73  82  77  81 /  20  40  70  90

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
.PR...NONE.
.VI...NONE.

&&

07

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SAN JUAN PR
624 AM AST THU APR 21 2005

PRZ001>013-AMZ710>750-221000-
624 AM AST THU APR 21 2005

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO.

.TODAY AND TONIGHT...SCATTERED TO NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS WILL CONTINUE TO AFFECT THE LOCAL ISLANDS TODAY AND
TONIGHT. SOME OF THESE SHOWERS AND STORMS WILL PRODUCE VERY HEAVY
RAINFALL...RESULTING IN FLASH FLOODING OF STREAMS...CREEKS...
STREETS...ROADS AND OTHER LOW LYING AREAS. IN ADDITION...SOME LARGER
LOCAL RIVERS WILL HAVE RAPID RISES AND MAY GO ABOVE FLOOD STAGE.
ALSO...MUDSLIDES ARE POSSIBLE OVER AREAS OF STEEP TERRAIN.

MODERATE NORTH NORTHEAST SWELLS WILL CONTINUE TO SUBSIDE ACROSS THE
LOCAL ATLANTIC WATERS AND THE CARIBBEAN PASSAGES THROUGH TODAY.
MARINERS SHOULD REMAIN ALERT FOR INTENSE SHOWERS AND THUNDERSTORMS.

.SPOTTER CALL TO ACTION STATEMENT...
SPOTTER ACTIVATION MAY BE REQUIRED.

.DAYS TWO THROUGH SEVEN...
A DEEP MID TO UPPER LEVEL TROUGH EXTENDING FROM THE WESTERN ATLANTIC
SOUTH ACROSS THE BAHAMAS AND INTO THE NORTH CENTRAL CARIBBEAN...WILL
REMAIN THE DOMINANT WEATHER FEATURE ACROSS THE LOCAL AREA THROUGH AT
LEAST SUNDAY. THIS FEATURE WILL COMBINE WITH AMPLE LOW LEVEL
MOISTURE AND VERY UNSTABLE CONDITIONS TO PRODUCE SHOWERS AND
THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL ACROSS THE LOCAL ISLANDS
FRIDAY. THIS TROUGH MAY ACTUALLY DEEPEN LOCALLY THROUGH THE
WEEKEND...WHILE THE MOISTURE AND INSTABILITY INCREASE FURTHER. THIS
PATTERN WILL RESULT IN ADDITIONAL SHOWERS AND THUNDERSTORMS WITH
VERY HEAVY RAINFALL. THEREFORE...THE LIKELIHOOD OF FLASH AND RIVER
FLOODING AND MUDSLIDES WILL CONTINUE TO INCREASE ACROSS THE LOCAL
ISLANDS. ALL LOCAL RESIDENTS AND VISITORS ARE URGED TO REMAIN ALERT
FOR THREATENING WEATHER AND FLOODING CONDITIONS THROUGH THE UPCOMING
WEEKEND.

VIZ001-002-AMZ710>730-221000-
624 AM AST THU APR 21 2005

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE U.S. VIRGIN ISLANDS.

.TODAY AND TONIGHT...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
WILL CONTINUE TO AFFECT THE LOCAL ISLANDS TODAY AND TONIGHT. SOME OF
THESE SHOWERS AND STORMS WILL PRODUCE LOCALLY HEAVY RAINFALL AND MAY
RESULT IN SOME FLOODING OF CREEKS...GUTS...STREETS...ROADS AND OTHER
LOW LYING AREAS.

MODERATE NORTH NORTHEAST SWELLS WILL CONTINUE TO SUBSIDE ACROSS THE
LOCAL ATLANTIC WATERS AND THE CARIBBEAN PASSAGES THROUGH TODAY.
MARINERS SHOULD REMAIN ALERT FOR INTENSE SHOWERS AND THUNDERSTORMS.

.SPOTTER CALL TO ACTION STATEMENT...
SPOTTER ACTIVATION MAY BE REQUIRED.

.DAYS TWO THROUGH SEVEN...
A DEEP MID TO UPPER LEVEL TROUGH EXTENDING FROM THE WESTERN ATLANTIC
SOUTH ACROSS THE BAHAMAS AND INTO THE NORTH CENTRAL CARIBBEAN...WILL
REMAIN THE DOMINANT WEATHER FEATURE ACROSS THE LOCAL AREA THROUGH AT
LEAST SUNDAY. THIS FEATURE WILL COMBINE WITH AMPLE LOW LEVEL
MOISTURE AND VERY UNSTABLE CONDITIONS TO PRODUCE SHOWERS AND
THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL ACROSS THE LOCAL ISLANDS
FRIDAY. THIS TROUGH MAY ACTUALLY DEEPEN LOCALLY THROUGH THE
WEEKEND...WHILE THE MOISTURE AND INSTABILITY INCREASE FURTHER. THIS
PATTERN WILL RESULT IN ADDITIONAL SHOWERS AND THUNDERSTORMS WITH
VERY HEAVY RAINFALL. THEREFORE...THE LIKELIHOOD OF FLASH AND RIVER
FLOODING AND MUDSLIDES WILL CONTINUE TO INCREASE ACROSS THE LOCAL
ISLANDS. ALL LOCAL RESIDENTS AND VISITORS ARE URGED TO REMAIN ALERT
FOR THREATENING WEATHER AND FLOODING CONDITIONS THROUGH THE UPCOMING
WEEKEND.

STAY TUNED TO NOAA WEATHER RADIO AND OTHER LOCAL MEDIA FOR FURTHER
DETAILS OR UPDATES.

FOR ADDITIONAL INFORMATION...VISIT THE NATIONAL WEATHER SERVICE WEB
SITE FOR PUERTO RICO AND THE U.S. VIRGIN ISLANDS AT (ALL LOWERCASE
LETTERS): HTTP://WWW.SRH.NOAA.GOV/SJU.