Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 300812
Area Forecast Discussion
National Weather Service San Juan PR
412 AM AST Thu Mar 30 2017
.SYNOPSIS...The proximity of an area of moisture associated with a
surface low well northeast of the region is expected to combine with
daytime heating and local effects to induce the development of
shower activity along and south of Cordillera Central this
afternoon. A generally fair weather pattern will prevail on tonight
Friday with some locally induced afternoon showers across west and
southwest Puerto Rico. Moisture advection is expected to increase
again during the upcoming weekend.
.SHORT TERM...Today through Saturday...
Partly cloudy to clear skies prevailed across the local islands
overnight. Some light passing showers were seen across the Atlantic
coastal waters.Some of these showers brushed the northern coast of
Puerto Rico. Rainfall accumulation with this activity was minimal.
For today, high pressure system will take control of the weather
conditions across the region. Drier air will continue to move across
the region from the north, limiting the development of showers
across the area. However, available moisture will combine once again
with daytime heating and local effect, will produce some showers
across the interior and southwest sections of Puerto Rico this
For late Friday into Saturday, an area of moisture is expected to
move from the Caribbean coastal waters to the north and is forecast
to affect the region Friday night into Saturday. Therefore, an
increase in shower activity is expected by that time.
.LONG TERM...Sunday through Thursday...
A surface high pressure across the central Atlantic is expected to
maintain a generally easterly trade wind flow across the region
through late in the weekend. This surface high is expected to drift
rapidly eastward while weakening as a strong surface low and
associated frontal boundary emerge across the eastern United States
seaboard early in the week. This feature is expected to maintain an
east to east northeast low level wind flow across the northeast
Caribbean through at least Tuesday. Another surface high will
develop across the central Atlantic by mid week between two low
pressure systems. One of the low across the north central Atlantic
and the other emerging across the northwestern Atlantic. The
combination of these features will induce a tight pressure gradient
over the region increasing the winds speed across the local islands
Wednesday and Thursday. Patches of moisture embedded in the trades
will combine each day with local effects to induce a new round of
showers and possible thunderstorms especially during the afternoons
hours across Puerto Rico, but not widespread precipitation is
expected. Looking well ahead we can see the repetition of the same
weather pattern of developing surface highs between surfaces lows
until at least the next weekend.
Model guidance suggest that the upper level ridge over the northeast
Caribbean is expected to erode during the weekend allowing more
moisture transport across the local islands Saturday, Sunday and
early in the week. This weakening upper ridge will allow old frontal
boundaries remnants to induce and increase in showers and possible
thunderstorms across the region until at least Monday.
.AVIATION...Mainly VFR conditions are expected to prevail across all
TAF sites through at least 30/16z. Some showers can be expected in
the vicinity of TJPS and TJMZ this afternoon. Low level winds will
be mainly north to northeast at 10 to 15 kts.
.MARINE...Early this morning buoy 41043 indicated a long period
northerly swell of 17 seconds with 7 feet seas. This swell is
expected to impact the Atlantic waters today and tonight, but is
expected to decay rapidly on Friday. This swell will induce a
high risk of rip currents for the northern beaches of PR. Two
additional northerly swells one associated to the surface low over
the Central Atlantic and another one from a low that should enter
the NW Atlantic on Saturday are expected to keep hazardous seas
and marine conditions at the northern coasts of the islands
through the weekend.
.PRELIMINARY POINT TEMPS/POPS...
SJU 83 75 85 76 / 20 20 20 20
STT 85 73 85 75 / 20 20 20 40
PR...High Rip Current Risk through this afternoon for North Central-
Northeast-Northwest-San Juan and Vicinity-Southeast-Western