Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 292010 CCA
Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
410 PM AST Wed Mar 29 2017
.SYNOPSIS...Shower and thunder development still possible across
the eastern interior and southern slopes through the early evening
hours. A generally fair weather pattern will prevail Thu and
Fri with some locally induced afternoon showers across west and
southwest Puerto Rico. Moisture advection is expected the upcoming
.SHORT TERM...Tonight through Sat Morning...
Shower and thunder development still possible through the early
evening hours across the eastern interior and southern slopes of
Puerto Rico. With the heaviest showers ponding of water on
roadways and in low lying areas is expected with some rises along
small stream and rivers.
As a surface low across the north central Atlantic moves east
northeast, a surface high will build north of the area. Therefore
low level winds are expected to become more east northeast Friday
and east to east southeast late Saturday and into Sunday. At upper
levels, a mid level ridge will build from the west and hold much of
the upcoming week. Precipitable water will continue to erode under
the prevailing northerly winds. As the low level winds becomes
easterly to east southeast the upcoming weekend, moisture is
expected to advect once again across the forecast area. Therefore,
tonight through Friday mainly fair weather conditions are expected
to prevail with a few locally induced showers across the west and
southwest Puerto Rico. As the moisture increases the upcoming
weekend, the chance for showers will increase, although under a
building ridge there will be hostile environment for thunderstorm
development. As a result, expect passing showers across the USVI and
E PR Saturday morning with showers developing over and west of the
Cordillera Saturday afternoon.
.LONG TERM...Sat thru Wed/issued 353 AM AST Wed Mar 29 2017/
A weak surface high pressure is expected to develop across the
central Atlantic early in the weekend to maintain an easterly
trade wind flow across the local islands Saturday and Sunday. At
the same time a surface low emerging across the northeastern
United States seaboard will push the surface high eastward while
weakening. As this happens patches of moisture associated with a
frontal remnants will combine with local effects both days to
produce an increase in cloudiness and shower activity across
Puerto Rico and the U.S. Virgin Islands during the weekend, but at
this time not widespread or significant precipitation is expected
during this period.
As the aforementioned surface low and associated frontal boundary
moves northeastward toward the north central Atlantic, another
stronger surface high is expected to develop and drift across the
western Atlantic. This feature will bring an east northeast trade
wind flow across the forecast area late Monday through at least
Wednesday. An upper level ridge is expected to build and
strengthening over the northeast Caribbean during the weekend and
is expected to persist over the region through at least Wednesday.
This feature will inhibit the development of widespread or deep
convection across the local islands during the forecast period,
but moisture embedded in the trades will continue to combine with
local effects to produce some shower activity across western and
interior Puerto Rico each day.
.AVIATION...Mostly VFR conds expected to prevail at all TAF sites
through the forecast period. VCTS expected at JPS/JSJ through
29/22z. Light northerly winds tonight and overnight becoming more
easterly by tomorrow.
.MARINE...Tranquil marine weather conditions will persist tonight
with seas below 5 feet and northerly winds at less than 15 knots.
A northerly swell is expected to reach the islands by Thursday.
Therefore the risk of rip currents is expected to increase along
the north facing beaches of PR and the USVI.
.PRELIMINARY POINT TEMPS/POPS...
SJU 75 84 74 84 / 30 30 20 20
STT 74 85 73 85 / 30 30 20 20