Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 230149
Area Forecast Discussion
National Weather Service San Juan PR
949 PM AST Wed Mar 22 2017
.UPDATE...Late tonight, an area of showers was seen across the
Caribbean waters moving northwest affecting the southeast sections
of Puerto Rico. This area of showers will continue to move across
the eastern half of Puerto Rico overnight. Favorable upper level
atmospheric conditions will aid new round of showers across the
area through early Thursday morning. Forecast is on track with
ongoing weather situation. No changes were needed to forecast
.AVIATION...Periods of showers will affect TJPS overnight. For
the rest of the TAF sites, VCSH are expected. Low level winds will
be mainly east to southeast at 10 kts.
.MARINE...Latest buoy observations continue to indicated seas up
to 7 feet across the offshore Atlantic waters. as a result, the
Small Craft advisory has been extended until 10 am AST Thursday.
.PREV DISCUSSION... /issued 245 PM AST Wed Mar 22 2017/
SYNOPSIS...A nearly stationary frontal boundary extending from
the north-central Atlantic southwest to the Windward Passage
between Hispaniola and Cuba. An Atlantic high pressure ridge
slowly moving east.
SHORT TERM...Tonight through Friday morning...Widely scattered
showers currently affecting the local area should diminish once
diurnal heating diminishes. Surface flow will continue from
southeast tonight and Thursday but will become more southerly and
lighter Thursday night and Friday as a strong low pressure system well
north over the northern Atlantic pulls a trough north from the
eastern Caribbean and over the area. This southeast to south flow
will bring increased moisture through the end of the work week. A
weak frontal boundary will hover to the north to enhance this
situation. A deepening upper level trough over cuba and jet north
of us will hold favorable divergence aloft. This will maintain
partly to mostly cloudy conditions with scattered showers.
Although heavy rains may occur in northwest Puerto Rico during the
afternoons, rains in general will be more probable on Friday with
isolated urban and small stream flooding possible.
LONG TERM...Friday night through day 8/issued 455 AM AST Wed Mar
Expect frequent periods of late evening and overnight passing
showers along portions of the north and east coastal sections of
the islands,followed by afternoon convection with enhanced shower
activity particularly across the interior and northern half of
Puerto Rico each day. The potential for periods of locally heavy
rainfall with minor urban and small stream flooding in isolated
areas will remain high across portions of the islands especially
for the northern and eastern half of Puerto Rico.
Long wave trough across the western Atlantic is still forecast to
deepen and extend southwards into the west and central Caribbean
Thru the end of the week . This will increase instability over the
northeastern Caribbean leading to enhanced upper level divergence
across the region. The subtropical jet and associated maxima will
continue to strengthen and to round the base of the upper trough which
will lift northeastward to just north of the region. The inverted
surface trough is to continue to amplify and lift northwards across
the region with a weak surface low now forecast to develop just north
Hispaniola by Monday. As a result, a moist south to southeasterly
flow should persist through Friday and into the weekend. All model
guidance support a very moist and unstable pattern across the region
for the next several days with good tropical moisture advection. Moisture
convergence along a frontal shear line, along with the lingering surface
trough and instability aloft will all favor high potential for enhanced
convection across the region at least through Tuesday of next week.
Winds are forecast to become more easterly by Wednesday as the surface
trough weakens and the upper trough fills and lifts north of the
region. This should then support a gradual decrease in moisture
transport. However, moisture along the old frontal shearline
should return across the region to allow for nocturnal shower
activity, and diurnally induced afternoon convection which should
be focused over the interior and west sections of PR.
AVIATION...Mountains obscurations with isolated areas of MVFR conds
with CIGS 020-030 are expected in central and northern PR affecting
mainly TJBQ/TJMZ. Elsewhere VFR conds will prevail. Winds sfc to
FL050 SE 10 to 15 kts. Maximum winds WSW 75 knots at FL400.
MARINE...Seas up to 7 feet are expected across the offshore
Atlantic waters tonight. Seas will diminish by thursday morning
however a larger northerly swell is expected to impact the
Atlantic waters and local passages by late Friday with
deteriorating conditions though the weekend.
.PRELIMINARY POINT TEMPS/POPS...
SJU 75 87 77 85 / 20 40 50 50
STT 75 85 74 84 / 30 30 50 50
PR...High Rip Current Risk through Thursday evening for Culebra-
Mayaguez and Vicinity-North Central-Northeast-Northwest-San
Juan and Vicinity-Southeast-Western Interior.
VI...High Rip Current Risk through Thursday evening for
St.Thomas...St. John...and Adjacent Islands.
AM...High Rip Current Risk through Thursday evening for Coastal
Waters of Northern USVI and Culebra out 10 NM-Coastal
Waters of Southern USVI Vieques and Eastern Puerto Rico out
Small Craft Advisory until 10 AM AST Thursday for Atlantic
Waters of Puerto Rico and USVI from 10 NM to 19.5N.