Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXCA20 KWBC 301200
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
659 AM EST FRI JAN 30 2015

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. POLAR TROUGH
OVER THE WESTERN ATLANTIC CONTINUES TO RAPIDLY LIFT TO THE
NORTHEAST AS ANOTHER TROUGH DEEPENS ACROSS THE EASTERN USA TO THE
WESTERN ATLANTIC. THE FORMER SUSTAINS A WANING FRONT TO THE NORTH
OF THE FORECAST AREA...WITH A PREFRONTAL SHEAR LINE MEANDERING
ACROSS PUERTO RICO AND THE USVI. THIS FAVORS ISOLATED CONVECTION
AND BRISK EAST-NORTHEASTERLY WINDS ACROSS THE NORTHEAST CARIBBEAN
ISLES. FRONT AND THE SHEAR LINE ARE EXPECTED TO WEAKEN DURING THE
DAY TODAY. MEANWHILE...NORTHEASTERLY WINDS ARE LIKELY TO FAVOR A
ROUND OF SCATTERED AFTERNOON CONVECTION ACROSS WESTERN INTERIOR
PORTIONS OF PUERTO RICO DURING THE DAY.

MID/UPPER TROUGH EXITING THE USA IS TO RAPIDLY AMPLIFY AS IT
ENTERS THE WESTERN ATLANTIC EARLY IN THE CYCLE. THE
TROUGH...HOWEVER...IS EXPECTED TO BOTTOM OUT ALONG
23N/24N...FARTHER TO THE NORTH THAN THE FORMER. AT LOW
LEVELS...SURFACE TROUGH QUICKLY SWINGS ACROSS THE WESTERN ATLANTIC
AS A POLAR RIDGE BUILDS BEHIND IT. LACKING UPPER LEVEL
SUPPORT...ASSOCIATED SURFACE FRONT IS TO THEN STALL TO THE NORTH
OF 20N/21N. THROUGH MIDDAY ON SUNDAY THE SURFACE RIDGE IS TO THEN
DOMINATE AREA WEST OF 50W AND NORTH OF 15N...FAVORING A TIGHT
GRADIENT AND BRISK EASTERLY TRADES. BUILDING RIDGE DRIVES A
PREFRONTAL SHEAR LINEA CROSS PUERTO RICO TO THE USVI DURING
AFTERNOON HOURS ON SATURDAY...WITH WINDS FORECAST TO BACK TO THE
NORTHEAST. THIS WILL RESULT IN A COOL ADVECTIVE PATTERN THAT IS
EXPECTED TO PERSIST THROUGH EARLY MONDAY MORNING WHEN THE
PREVAILING EASTERLY TRADES RETURN TO THE FORECAST AREA. MOST
ACTIVE CONVECTION IS EXPECTED ON SATURDAY TO SUNDAY AS THE SHEAR
LINE ENTERS THE FORECAST AREA...WITH GLOBAL MODEL GUIDANCE SHOWING
MAXIMA OF LESS THAN AN INCH IN SCATTERED CONVECTION. THE HIGHER
RESOLUTION MODELS ARE A BIT MORE OPTIMISTIC...SHOWING MAXIMA OF
2-3 INCHES CLUSTERING OVER WESTERN INTERIOR PORTIONS OF PUERTO
RICO. BUT FOR THE MOST PART EXPECTING RAINFALL AMOUNTS TO RANGE
BETWEEN A QUARTER TO HALF AN INCH.

BROAD MID/UPPER LEVEL RIDGE IS TO THEN ESTABLISH DURING THE MEDIUM
RANGE PERIOD...TO HOLD THROUGH THE REST OF THE WEEK. THIS IS TO
STRENGTHEN THE TRADE WINDS CAP AND LEAD TO GRADUAL EROSION OF
AVAILABLE MOISTURE.

JN BAPTISTE...MS (SAINT LUCIA)
NANDA...MDS (SURINAME)
DAVISON...WPC (USA)
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.