Debris Flows in Puerto Rico, March 6 to 9, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
250 PM AST SAT MAR 6 2010

.SYNOPSIS...MEANDERING COLD FRONT AND ASSOCIATED SHEAR LINE TO
MOVE ERRATICALLY AND SLOWLY NEXT 3 DAYS RESULTING IN MOSTLY CLOUDY
CONDITIONS WITH PERIODS OF RAINFALL...SOMETIMES HEAVY...THROUGH
EARLY NEXT WEEK. UPPER TROUGH MOVES NORTH OF AREA SUNDAY...BUT LOW
LEVEL MOISTURE LEFT BEHIND MAY LINGER AS LONG AS THROUGH THE
MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...HEAVY RAIN TO AFFECT NORTHEASTERN TO SOUTHEASTERN PR
AND THE US VIRGIN ISLAND THIS EVENING.

(NEAR TERM) VERY COMPLEX PATTERN UNDERWAY. SATELLITE
IMAGERY AND DEW POINT OBS POINT TO AN IRREGULARLY SHAPED COLD FRONT
DIGGING INTO THE SOUTH CENTRAL CARIBBEAN IN A LINE UP TOWARDS
SANTO DOMINGO CONTINUING NE TOWARDS BUOY 41403...200 MI NORTH OF ST
THOMAS (MEANING TO THE NORTH AND WEST OF PR). THIS SEEMS EVIDENCED
BY DEW POINTS IN THE LOW TO MID 60S TO THE LEFT (W-NW) OF THIS
JAGGED LINE...AND STILL IN THE LOW TO MID 70S TO THE RIGHT (E-SE
INCLUDING ALL OF PR/USVI AS OF 18Z). TO FURTHER COMPLICATE
THINGS...SHEAR LINE (AREA OF BEST CONVERGENCE...MOST WEATHER) APPEARS
TO BE HOOKING INTO THE SOUTHERN FLANK OF THE COLD FRONT AT 15.5N
72.5W (EXPERIENCING DEEP CONVECTION AT 18Z)...RUNNING
NORTHEASTWARD ROUGHLY IN A LINE GOING SOUTH OF MAINLAND PR BETWEEN
ST CROIX AND PR. RADAR AT 18Z SHOWED SOMEWHAT DEEPER CONVECTION
AND HEAVY RAIN ALONG THIS LINE...WHICH HAS NOT IMPACTED LAND
MASSES THUS FAR. THIS MAY BE CONFUSING...BUT PRESENTS A
SIGNIFICANT FORECAST ISSUE. BEHIND THE TRUE COLD FRONT BOUNDARY
(HISPANIOLA) ONE WOULD EXPECT TYPICALLY MORE STABLE COOL
ADVECTION...WHICH IS VERIFYING PER CURRENT OBS. HOWEVER...ALONG
THE SHEAR LINE CURRENTLY DRAPED TO THE SE OF PR MOISTURE
CONVERGENCE IS VERY HIGH AND COULD EVEN MEANDER A BIT BACK TOWARDS
MAINLAND PR THIS EVENING MAKING HEAVY RAIN A GREATER THREAT. MAJOR
QUESTION IS...WHERE WILL THE SHEAR LINE BE THROUGH 24 HOURS (OR
FOR THAT MATTER UP TO 72 HOURS)...AND WILL THE COLD AIR CATCH UP.

GOOD NEWS IS THAT MODELS HAVE COME IN LINE AND BOTH GFS AND NAM12
INITIALIZE THE SHEAR LINE MORE OR LESS WHERE WE HAVE IT MENTIONED
ABOVE...AND PROGRESSING IT SOUTHEASTWARD THROUGH 24 HOURS. THAT
WOULD RESULT IN BEST CONVERGENCE THIS EVENING (MOST ACTIVE PERIOD
EXPECTED IN THE NEAR TERM) OVER EXTREME ERN PR AND FOCUSED OVER
THE USVI. WILL SHIFT POPS AND WEATHER A BIT EAST AND MAY EXTEND
THE FFA TO ST CROIX TO ACCOUNT FOR THAT POSSIBILITY.

BACK TO THE COLD FRONT...BOTH MODELS INITIALIZING PRE FRONTAL THETA
E RIDGING OVER THE FA WITH TRUE THETA E PACKING (COLD FRONT) OVER
EASTERN DOMINICAN REP AND OUT OVER THE ALTC WATERS A GOOD 100 MI
NORTH OF PR. FIRST WAVE (WEAKER PORTION) OF THIS BOUNDARY TO MOVE
OVER THE NORTHERN HALF OF PR/USVI OVERNIGHT...WITH NORTHERLY LOW
LEVEL FLOW BEHIND IT...AND LAND BREEZE TO ENHANCE CONVERGENCE OVER
NRN PR AFTER 22Z. TO SUM IT ALL UP...SITUATION FAVORABLE FOR HEAVY
RAIN TO BUILD AND MOVE VERY SLOWLY OVER NRN PR AFTER 22Z...WITH
SHEAR LINE PUSHING EAST OF VI ALSO PROVIDING THE THREAT OF HEAVY
CONVECTION DOWN TO ST CROIX. THINK THE FFA IS GOOD WHERE IT IS
CURRENTLY LOCATED OVER NRN PR AND WILL EXTEND TO COVER ST CROIX
AND SOUTHEASTERN PR ZONE. SEVERAL FACTORS COULD SHIFT AREAS OF HEAVY
RAIN...INCLUDING THE SHORT WAVE FIRING DEEP CONVECTION OVER 15.5N
72.5W AND THE ABILITY FOR THE COLD AIR BOUNDARY TO DIG SOUTH.

(SUNDAY THROUGH LONG TERM)...BY THIS TIME SHEAR LINE WILL BE OUT
OF CWA...BUT COLD AIR BOUNDARY WILL WOBBLE WITH 2ND SHOT OF COLDER
AIR TO PUSH OVER PR/USVI BY 00Z MONDAY. AGAIN...TIMING OF THIS A
MAIN CONCERN...THE QUICKER IT MOVES THE LESS CHANCE OF DEEP
CONVECTION TOMORROW...THE SLOWER IT MOVES THE GREATER. ALSO DURING
THE DAY SUNDAY...THE UPPER LEVEL PORTION OF THE DEEP POLAR TROUGH
DIGS TO ITS SOUTHERNMOST POINT AND PUSHES JUST NORTH OF THE AREA
FROM WEST TO EAST. BEST U/L JET DYNAMICS WILL REMAIN ABOUT 100
MILES NORTH OF THE AREA...HOWEVER...IF ANY LOW LEVEL MECHANISMS
CAN FORCE DEEP CONVECTION TOMORROW...THEN ENHANCEMENT VIA THE
UPPER TROUGH IS VERY LIKELY. LOOKING AHEAD TO NEXT WEEK GFS SHOWS
RETROGRESSION OF LOW LEVEL MOISTURE ASSOCIATED WITH THE PRE
FRONTAL TROUGHINESS TO WORK BACK OVER AREA TUESDAY AND WED AND
WHICH COULD POSSIBLY RESULT IN BETTER CONDITIONS MONDAY...BUT BACK
TO MOSTLY CLOUDY WITH LIGHT RAIN FOR TUE/WED.

&&

.AVIATION...EXPECT MVFR TO LOCALLY IFR CONDITIONS WITH MOUNTAIN
OBSCURATIONS TO PREVAIL ACROSS MOST OF THE LOCAL ISLANDS AND TAF
SITES THROUGH 24 HOUR CYCLE. HEAVIEST RAIN AND MOST LIKELY IFR
CONDITIONS TO BE FOR TJSJ...TIST AND TISX 22Z-10Z.

&&

.MARINE...BUOYS AND LOCAL DATA REPORTS NOT REALLY ADDING UP TO HIGH SURF
ADVISORY CONDITIONS. ALTHOUGH BUOY 41043 SHOWING 7.5 FOOT SWELL
STEADY AT 10 SEC...BUOY 41406 (200 MILES NORTH OF THE TURKS/CAICOS)
ONLY SHOWING 4.5 FOOT SWELL...AND FEEL THAT THE 41406 OB IS MORE
REPRESENTATIVE OF WHATS HITTING NRN PR/USVI GIVEN MORE NORTH
NORTHWESTERLY DIRECTION. EVEN IF WE HEDGED TOWARDS AN
AVERAGE...THE MAX BREAKING WAVE HEIGHT WOULD STILL ONLY BE AROUND
10 FEET...WITH MOST PLACES LIKELY ONLY EXPERIENCING BREAKERS OF 6
TO 8 FEET. FOR THAT REASON WILL CANCEL THE HIGH SURF ADVISORY.
NONETHELESS...SEAS WILL CONTINUE QUITE CHOPPY AND STILL HAZARDOUS
TO MARINERS...BUT NOT GREATER THAN 10 FOOT BREAKERS (HIGH SURF
CRITERIA). BEACH GOERS SHOULD STILL BE CAUTIOUS...AS CONDITIONS
WILL REMAIN BORDERLINE FOR SEVERAL DAYS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  80  72  81 / 100  70  50  40
STT  74  81  73  83 /  90  60  50  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...FLASH FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR CENTRAL INTERIOR-
     CULEBRA-EASTERN INTERIOR-NORTH CENTRAL-NORTHEAST-SAN JUAN
     AND VICINITY-SOUTHEAST-VIEQUES.

VI...FLASH FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR ST CROIX-ST.
     THOMAS/ST. JOHN/ADJACENT ISLANDS.

&&

06/93

HAZARDOUS WEATHER OUTLOOK FOR PUERTO RICO AND THE U.S. VIRGIN
ISLANDS
NATIONAL WEATHER SERVICE SAN JUAN PR
725 AM AST SAT MAR 6 2010

AMZ710>745-PRZ001>013-071000-
SAN JUAN AND VICINITY-NORTHEAST-SOUTHEAST-EASTERN INTERIOR-
NORTH CENTRAL-CENTRAL INTERIOR-PONCE AND VICINITY-NORTHWEST-
WESTERN INTERIOR-MAYAGUEZ AND VICINITY-SOUTHWEST-CULEBRA-VIEQUES-
THE NEARSHORE AND OFF SHORE ATLANTIC AND CARIBBEAN COASTAL WATERS-
725 AM AST SAT MAR 6 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO AND THE
ADJACENT COASTAL WATERS.

.DAY ONE...TODAY AND TONIGHT

A FLASH FLOOD WATCH IS IN EFFECT FOR PARTS OF PUERTO RICO. PLEASE
REFER TO LATEST FLOOD WATCH MESSAGE FOR MORE DETAILS. A HIGH SURF
ADVISORY ALSO REMAINS IN EFFECT UNTIL EARLY SUNDAY.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

A FLASH FLOOD WATCH IS IN EFFECT FOR PARTS OF PUERTO RICO. PLEASE
REFER TO LATEST FLOOD WATCH MESSAGE FOR MORE DETAILS.

.SPOTTER INFORMATION STATEMENT...

REPORTS OF HEAVY RAINFALL OR FLOODING WOULD BE GREATLY APPRECIATED.

AMZ715-725-VIZ001-002-071000-
ST. THOMAS ST. JOHN ADJACENT ISLANDS-ST CROIX-
NEARSHORE ATLANTIC AND ADJACENT CARIBBEAN COASTAL WATERS-
725 AM AST SAT MAR 6 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE U.S. VIRGIN ISLANDS AND
THE ADJACENT COASTAL WATERS.

.DAY ONE...TODAY AND TONIGHT

A FLASH FLOOD WATCH IS IN EFFECT FOR ST. THOMAS AND ST. JOHNS.
PLEASE REFER TO LATEST FLOOD MESSAGE FOR MORE DETAILS. A HIGH SURF
ADVISORY ALSO REMAINS IN EFFECT UNTIL EARLY SUNDAY.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

A FLASH FLOOD WATCH IS IN EFFECT FOR ST. THOMAS AND ST. JOHNS.
PLEASE REFER TO LATEST FLOOD MESSAGE FOR MORE DETAILS. A HIGH SURF
ADVISORY ALSO REMAINS IN EFFECT FOR THE SAME AREA UNTIL EARLY
SUNDAY.

.SPOTTER INFORMATION STATEMENT...

REPORTS OF HEAVY RAINFALL OR FLOODING WOULD BE GREATLY APPRECIATED.