Flash Flood Warning 20, NWS JSJ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
402 PM AST THU APR 6 2006

.SYNOPSIS...PUERTO RICO LIES UNDER THE RIGHT ENTRANCE REGION OF AN
UPPER LEVEL JET MOVING TOWARD THE NORTHEAST. DURING THE NEXT 48
HOURS THAT JET WILL DRIFT SOUTH INTO THE CARIBBEAN. LATE ON FRIDAY
AND UPPER LEVEL TROUGH WILL PASS THROUGH...FOLLOWED BY AN UPPER
LEVEL RIDGE ON SATURDAY NIGHT. DURING THE MIDDLE OF NEXT WEEK
ANOTHER TROUGH WILL APPROACH THE AREA WITH AN UPPER LEVEL JET
PASSING BY THE ISLANDS WEDNESDAY NIGHT. THE TROUGH...HOWEVER IS
EXPECTED TO DELAY UNTIL FRIDAY NIGHT OF NEXT WEEK.

AT MID LEVELS...A TROUGH WILL PASS...MOSTLY TO THE NORTH TONIGHT.
HIGH PRESSURE THEN BUILDS OVER THE AREA THROUGH SATURDAY NIGHT.
FLOW BECOMES SOUTHWEST ON SUNDAY NIGHT. A SHORT WAVE IS FORECAST
TO ARRIVE THURSDAY EVENING OF NEXT WEEK...FOLLOWED BY A TROUGH
PASSAGE ON FRIDAY NIGHT. AT THE SAME TIME HIGH PRESSURE BUILDS
INTO THE GULF OF MEXICO.

AT LOWER LEVELS...BROAD HIGH PRESSURE STRETCHES FROM THE CAROLINAS
IN THE EASTERN UNITED STATES TO NEAR THE AFRICAN COAST. WITH HIGH
PRESSURE IN THE CENTRAL ATLANTIC WEDGED BETWEEN A LOW NEAR THE
AZORES AND A LOW OVER NEWFOUNDLAND. HIGH PRESSURE THEN DEVELOPS IN
THE NORTHEAST ATLANTIC OVER THE WEEKEND EXTENDING INTO THE
CARIBBEAN. AFTER A LOW PRESSURE MOVES NORTHEAST OUT OF THE WESTERN
ATLANTIC ON THE FIRST OF THE WEEK HIGH PRESSURE DOMINATES THE
WESTERN ATLANTIC THROUGH FRIDAY. EARLY NEXT WEEK AN AREA OF
MOISTURE MOVES IN FROM THE EAST NORTHEAST AND CROSSES PUERTO RICO
AND THE U.S. VIRGIN ISLANDS SUNDAY NIGHT AND MONDAY. ALTHOUGH
FRONTS DO NOT APPEAR TO SINK TO OUR LATITUDE...A GENERAL
TROUGHINESS WILL EXIST IN THE AREA LATER NEXT WEEK ACCOMPANIED BY
LOW LEVEL MOISTURE.

&&

.DISCUSSION...SHOWERS DEVELOPED EARLY UNDER FLASH FLOOD WATCH
CONDITIONS AND WERE SCATTERED OVER A FAIRLY WIDE PORTION OF
NORTHEAST PUERTO RICO AND MOST OF THE INTERIOR MUNICIPALITIES.
STREAMERS FORMED OFF OF MOST OF THE PUERTO RICAN AND VIRGIN
ISLANDS AND SOME OF THESE IMPACTED CEIBA AND FAJARDO WHERE RIO
FAJARDO ROSE ABOVE FLOOD STAGE THIS AFTERNOON. OTHERWISE MOST OF
THE SHOWERS LACKED THE FOCUS THAT STORMS HAD YESTERDAY...RESULTING
IN LOWER MAXIMUM RAINFALL AMOUNTS BUT MORE WATER IN GENERAL
RELEASED OVER THE AREA. COUPLED WITH PREVIOUS RAINS...THIS CAUSED
A NUMBER OF RIVERS INCLUDING THE RIO CANAS TO RISE AS RAINS
CONTINUED IN THE INTERIOR OF PUERTO RICO DURING THE AFTERNOON.

THE GFS INDICATES THAT BOTH RELATIVE HUMIDITY AND PRECIPITABLE
WATER WILL BE COMING DOWN TONIGHT THROUGH SUNDAY. SATURDAY SHOULD
BE CONSIDERABLY DRIER WITH DOWNWARD VERTICAL MOTION INDICATED OVER
THE AREA.

CURRENTLY THE GFS ALSO HAS A BULLS EYE OF MOISTURE MOVING OVER
PUERTO RICO AND THE U.S. VIRGIN ISLANDS ON SUNDAY NIGHT. THIS CAN
APPARENTLY BE TRACED IN THE MODELS BACK TO AN AREA OF MOISTURE
THAT IS CURRENTLY VISIBLE IN THE SATELLITE IMAGERY AT 21 NORTH
LATITUDE 46.5 WEST LONGITUDE. IT WEAKENS ON SATURDAY BUT THEN
REGENERATES ON SUNDAY. IF MODEL SOLUTIONS HOLD THEN THIS COULD
YIELD SIGNIFICANT RAINFALL FOR THE ENTIRE AREA SUNDAY NIGHT AND
MONDAY MORNING. CONDITIONS ON TUESDAY IMPROVE...HOWEVER...AND
DRYING FOLLOWS. ON THURSDAY NIGHT OF THE NEXT WEEK AND
FRIDAY...MOISTURE AGAIN INCREASES...BUT CURRENTLY IT IS FORECAST
TO HOLD JUST SOUTH OF PUERTO RICO. IT IS TOO FAR OUT TO TELL MUCH
ABOUT THIS BUT SAINT CROIX COULD RECEIVE RAINS IN THIS TIME
PERIOD AND SOME INCREASE IN SHOWER ACTIVITY IS POSSIBLE OVER THE
REST OF THE FORECAST AREA.

&&

.MARINE...SEAS WILL CONTINUE TO DIMINISH A LITTLE THROUGH FRIDAY
AND THEN PEAK NEAR 5 TO 6 FEET ON SUNDAY. SOME NORTHEAST SWELL
WILL CONTINUE THROUGH THE END OF THE WEEK.

&&

.AVIATION...THERE WILL LIKELY BE YET ONE MORE DAY OF WIDESPREAD
CONVECTION OVER THE AREA AS THE JET ALOFT SLOWLY SINKS OVER THE
AREA EVEN AS WINDS SPEEDS ARE DECREASING AT UPPER LEVELS. THEN ON
SATURDAY CONDITIONS SHOULD BE GREATLY IMPROVED. A FRONTAL SYSTEM
WILL APPROACH FROM THE NORTHWEST BEGINNING MID WEEK AND MAY
PRESENT SOME INCLEMENT WEATHER EN ROUTE FROM SAN JUAN TO MIAMI FROM
THE MIDDLE OF THE WEEK THROUGH FRIDAY OR SATURDAY.

&&

.HYDROLOGY...THE FLASH FLOOD WATCH WILL EXPIRE AT 8 PM AND THE
DECISION AS TO WHETHER IT WILL BE NEEDED BEYOND THEN WILL BE
DEFERRED UNTIL CLOSER TO THAT TIME. NEVERTHELESS...SOME RIVERS
WILL STILL BE RISING AT THAT TIME THOUGH THEY MAY NOT FLOOD WITH
THE RAINFALL THAT HAS FALLEN. THIS SITUATION WILL NEED TO BE
MONITORED CLOSELY...AND FLOODING WILL DEPEND ON HOW LATE SHOWERS
PERSIST INTO THE EVENING.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  74  83  74  83 /  70  70  50  50
STT  76  82  76  82 /  50  50  20  20

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...FLASH FLOOD WATCH UNTIL 8 PM AST THIS EVENING FOR PRZ001-PRZ002-
     PRZ004-PRZ005-PRZ006-PRZ008-PRZ009-PRZ010-PRZ012-PRZ013.

VI...NONE.

&&

SNELL

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE SAN JUAN PR
600 AM AST THU APR 6 2006

PRZ001>013-AMZ710>750-071000-
600 AM AST THU APR 6 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO.

.TODAY AND TONIGHT...ABUNDANT LOW LEVEL MOISTURE...AN APPROACHING
UPPER LEVEL TROUGH...AND LOCAL EFFECTS...WILL COMBINE TO PRODUCE
NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS TODAY. THESE SHOWERS
AND THUNDERSTORMS HAVE THE CAPABILITY OF PRODUCING HEAVY RAINFALL...
ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS. THE POTENTIAL FOR
FLASH FLOODING ACROSS THE INTERIOR AND NORTHERN PORTIONS OF THE
ISLAND TODAY IS ELEVATED DUE TO RECENT RAINS THAT HAVE SATURATED THE
SOIL AND RAISED THE LEVELS OF MANY RIVERS. FOR THIS REASON...A FLASH
FLOOD WATCH HAS BEEN ISSUED THIS MORNING FOR THE INTERIOR AND
NORTHERN PORTIONS OF PUERTO RICO...AND INCLUDING CULEBRA AND
VIEQUES...THROUGH 8 PM AST.

.DAYS TWO THROUGH SEVEN...ABUNDANT MOISTURE WILL CONTINUE TO ENHANCE
LOCAL DIURNAL SHOWER ACTIVITY AGAIN ON FRIDAY. THIS WILL PRODUCE
CONDITIONS FAVORABLE FOR THE GENERATION OF AFTERNOON SHOWERS AND
THUNDERSTORMS IN WESTERN PUERTO RICO WHICH WILL BE CAPABLE OF
GENERATING URBAN AND SMALL STREAM FLOODING. NO OTHER HAZARDOUS
WEATHER IS EXPECTED.

.SPOTTER CALL TO ACTION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED.

VIZ001-002-AMZ710>730-071000-
600 AM AST THU APR 6 2006

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

.TODAY AND TONIGHT...ABUNDANT LOW LEVEL MOISTURE TODAY...COMBINED
WITH AN UPPER LEVEL TROUGH APPROACHING THE REGION...WILL COMBINE TO
PRODUCE CONDITIONS FAVORABLE FOR THE GENERATION OF AFTERNOON SHOWERS
AND POSSIBLY A THUNDERSTORM. THESE SHOWERS AND THUNDERSTORMS HAVE
THE POTENTIAL OF PRODUCING HEAVY RAINFALL...ESPECIALLY DURING THE
AFTERNOON AND EVENING HOURS...CAPABLE OF GENERATING URBAN AND SMALL
STREAM FLOODING.

.DAYS TWO THROUGH SEVEN...ABUNDANT MOISTURE WILL CONTINUE TO ENHANCE
LOCAL SHOWER ACTIVITY AGAIN ON FRIDAY. THIS WILL PRODUCE CONDITIONS
FAVORABLE FOR THE GENERATION OF HEAVY AFTERNOON SHOWERS CAPABLE OF
GENERATING URBAN AND SMALL STREAM FLOODING. NO OTHER HAZARDOUS
WEATHER IS EXPECTED.

.SPOTTER CALL TO ACTION STATEMENT...

SPOTTER ACTIVATION IS MAY BE REQUIRED.

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.

SR