San Juan Discussion
Posted by JAC on 8/31/2009, 7:31 am
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
430 AM AST MON AUG 31 2009

.SYNOPSIS...TUTT LOW NORTH OF PR WILL DRIFT TO THE WEST SOUTHWEST
AND SETTLE OVR HISPANIOLA BY TONIGHT. UPPER LVL RIDGE OVR THE TROP
ATLC WILL BUILD WWD INTO THE ERN CARIBBEAN TUE THROUGH WED AND
MAINTAIN A SUBSIDENT PATTERN ACROSS THE REGION. MEANWHILE...BROAD
AREA OF LOW PRES ALONG 50W THIS MORNING WILL TRACK SLOWLY TO THE
WNW OVER THE NEXT SVRL DAYS AND MOVE ACROSS THE REGIONAL WATERS
THU NIGHT.

&&

.DISCUSSION...MODELS SHOW TUTT LOW DRIFTING TO WEST SOUTHWEST WITH
SUBSIDENCE INCREASING TOWARD THE END OF THE DAY. HAVE TRENDED
POPS DOWNWARD FOR TODAY BUT STILL ANTICIPATING ISOLD/SCT STRONG
CONVECTION OVR WRN PR THIS AFTERNOON. SUBSIDENCE/DRYING INCREASES
ON TUE AND HOLDS THROUGH WED AS MID-UPPER LVL RIDGING BUILDS FROM
THE EAST FURTHER LIMITING PRECIP CHANCES. SFC WINDS TURN MORE TO
THE NORTHEAST SO HAVE LIMIT POPS TO THE SOUTHWEST CORNER OF PR.

FORECAST FOR THU THROUGH FRI IS HIGHLY DEPENDENT ON
TRACK/EVOLUTION ON BROAD AREA OF LOW PRES ALONG 50W THIS MORNING.
HAVE FOLLOWED THE 00Z ECMWF CLOSELY DURING THIS TIME FRAME AS IT
HAS BEEN THE MOST CONSISTENT/RELIABLE MODEL THIS YEAR AND ALSO WITH
THIS SYSTEM TAKING IT ACROSS THE WATERS JUST NORTH OF PR/USVI OVER
THE PAST FOUR DAYS AS A WEAK TROPICAL CYCLONE. NOGAPS AND CANADIAN
MODELS ALSO DEVELOP THIS SYSTEM WHILE GFS/UKMET DO NOT. PER NHC
TWO PRODUCT...CONDITIONS STILL APPEAR FAVORABLE FOR FURTHER
DEVELOPMENT. IN ADDITION...THE FIRST FEW SATELLITE IMAGES AFTER
THE ECLIPSE SHOW THUNDERSTORMS BECOMING MORE CONCENTRATED NEAR THE
CENTER. GIVEN THAT WE ARE ALMOST AT THE PEAK OF THE HURRICANE
SEASON AND AT LEAST MARGINALLY FVRBL CONDITIONS I WOULD EXPECT AT
LEAST A NAMED STORM AND NHC IS GIVING IT A HIGH CHANCE OF
DEVELOPING INTO A TROPICAL CYCLONE. PLEASE REFER TO NHC PRODUCTS
FOR MORE DETAILS ON THIS SYSTEM.

THERE IS A GREAT DEAL UNCERTAINTY HERE ESPECIALLY WITH RESPECT TO
TIMING AND INTENSITY ALTHOUGH NOT AS EXTREME AS YESTERDAY. THE
EARLY TRACK NHC MODELS SHOW THE SYSTEM ONLY TO ABOUT 61W BY FRI
EVENING WHILE THE 00Z ECWMF SHOWS THE SYSTEM ALMOST TO 70W BY THIS
TIME. THE ECMWF LOOKS MORE REASONABLE WHEN COMPARED TO
CLIMATOLOGY AS A SYSTEM THAT IS ALREADY AT 50W WOULD ONLY TAKE ON
AVERAGE A MAXIMUM OF FOUR DAYS TO GET TO THE LONGITUDE OF PR
MOVING AT THE CLIMO RATE OF SPEED OF 10 KNOTS BUT EVEN THE ECMWF
SHOWS THE SYSTEM SLOWING DOWN TOO WHEN IT REACHES 55W. HAVE
ADJUSTED GRIDS THU-FRI TO ADD MORE WX/POPS AND INCREASE WINDS AND
SEAS.

&&
70
In this thread:
Another DMAX Flare for 94L - JAC, 8/31/2009, 6:40 am
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