Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 011555
Area Forecast Discussion
National Weather Service San Juan PR
1155 AM AST Wed Mar 1 2017
.UPDATE...The latest guidance and observations were enough to make
us slightly tweak the forecast for this afternoon. The higher
afternoon pops are now for the western interior and western
sections of PR, trending slightly to the SW. Otherwise the rest of
the local area should observe isolated showers. Winds will
continue to be mainly from the east at about 15-20KT with
occasional gusts and sea breeze variations. No other changes were
.AVIATION...VFR conds expected through the forecast period. E
winds at 15-20KT with occasional gusts expected as well as some
variations in winds due to sea breeze component. SHRA possible
this afternoon which could cause VCSH at TJMZ and TJBQ. Winds to
decrease slightly after 02/02Z and VCSH possible due to passing
brief SHRA over the local area.
.MARINE...Small craft advisories and high risk of rip currents
continue through the local area. There were no changes from the
previous discussion. Latest guidance still suggest hazardous seas
through the end of the workweek.
.PREV DISCUSSION... /issued 427 AM AST Wed Mar 1 2017/
SYNOPSIS...Broad upper trough north and east of the region will become
amplified and sink south across the northeast Caribbean through Thursday.
The local islands should however remain the subsident side of the trough.
The trough will then fill and lift northward on Friday into the weekend.
Mid level ridge will continue to hold and build across the northeast
Caribbean into the upcoming weekend. Strong surface high pressure
will continue to build and spread eastward into the central Atlantic
and north of the region through Friday. This will maintain a tight
local pressure gradient and moderate to strong easterly trade
DISCUSSION...The strong easterly trades will transport fragment
of shallow low level moisture across the region through at least
Thursday. This will allow for occasional periods of passing
showers with brief gusty winds especially during the late evening
and overnight hours. During the day shower activity should
diminish across the north and eastern sections of the islands
leaving partly cloudy to mostly sunny skies and fresh easterly
trade winds. Afternoon showers should be then focused more over
part of the central and west sections of Puerto Rico, and on the
lee side of the rest of the islands. The shower activity should be
in the form of streamer like convection, therefore no significant
rainfall accumulations are expected the shower activity should be
fast moving and of short duration.
By Friday and into the weekend the local pressure gradient should
weaken in response to the high pressure ridge shifting farther east
across the Atlantic and a cold front entering and moving across
the west Atlantic. Therefore expect lesser moisture transport in
the decreasing easterly trade winds which in turn will result in
lesser amounts of late evening and early morning passing shower
activity with somewhat drier conditions for Friday and Saturday.
By sunday and into early next week, winds are to become more
northeasterly as high pressure ridge will build once again across
the west Atlantic. This pattern will bring periods of early morning
showers due to low level moisture convergence and the increasing
northeast trade winds.
AVIATION....Brief MVFR conditions will be possible until 01/15z in
the Leeward Islands otherwise VFR conditions will prevail across the
flying area through the forecast period. VCSH in SCT SHRA are
expected across TJSJ, TIST, TISX, TNCM and TKPK today but decreasing
aft 01/15z. SCT SHRA will dvlp btwn 01/18-22Z wrn/swrn PR with some
mtn obscurations. Winds will be mainly from the ENE at 15-30 kts
below FL180. Maximum winds west at 40 kts at FL410 at 02/00z.
MARINE...Moderate to fresh easterly winds will persist across most
of the regional waters except for the local passages and offshore Atlantic
and Caribbean waters, where winds may become fresh to locally strong
at times. The wind driven seas will create hazardous marine conditions
through the end of the work week.
The moderate to strong trade winds will cause seas to rise and
therefore increase the risk of strong rip currents on the north
and east facing beaches of Puerto Rico, Culebra,Vieques and St
.PRELIMINARY POINT TEMPS/POPS...
SJU 83 75 85 75 / 60 30 30 40
STT 86 74 85 74 / 40 40 40 30
PR...High Rip Current Risk through Thursday afternoon for Central
Interior-Culebra-North Central-Northeast-Northwest-San Juan
and Vicinity-Southeast-Vieques-Western Interior.
Small Craft Advisory until 8 PM AST Thursday for Southeast.
VI...High Rip Current Risk through Thursday afternoon for St Croix.
Small Craft Advisory until 8 PM AST Friday for St.Thomas...St.
John...and Adjacent Islands.
AM...High Rip Current Risk through Thursday afternoon for Coastal
Waters of Southern Puerto Rico out 10 NM.
Small Craft Advisory until 8 PM AST Thursday for Coastal Waters
of Southern Puerto Rico out 10 NM.
Small Craft Advisory until 8 PM AST Friday for Anegada Passage
Southward to 17N-Atlantic Waters of Puerto Rico and USVI
from 10 NM to 19.5N-Caribbean Waters of Puerto Rico from 10
NM to 17N-Coastal Waters of Northern Puerto Rico out 10 NM-
Coastal Waters of Northern USVI and Culebra out 10 NM-
Coastal Waters of Southern USVI Vieques and Eastern Puerto
Rico out 10 NM-Mona Passage Southward to 17N.