Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 291603
Area Forecast Discussion
National Weather Service San Juan PR
1203 PM AST Wed Mar 29 2017
Mostly sunny skies with little or no shower activity prevailed
today in Puerto Rico and the U.S. Virgin Islands. A northerly wind
flow combined with the lingering moisture, diurnal heating and sea
breeze variations will result in afternoon convection over the
eastern interior and southeast sections of Puerto Rico and downwind
from the U.S. Virgin Islands. The morning package was updated to
introduce a light to moderate risk of Flooding rain over the east
interior and southeastern sections of Mainland Puerto Rico.
Most of the SHRA/TSRA are expected downwind from TJSJ/TIST/TISX
this afternoon. However, passing -SHRA/SHRA are possible across
these terminals from time to time through the FCST PRD. TJBQ/TJMZ
can expect VFR conditions most of the period. SHRA/+SHRA with VCTS
and BKN-OVC ceiling btwn FL020-FL070 expected across TNCM/TKPK/
TJPS btwn 29/16-22z. SHRA should diminish across the terminals
after 29/23z. Sfc winds from the N around 10 knots with sea
breeze variations til 29/22z, then calm to light and VRB winds.
Tranquil marine weather conditions will persist today with seas
below 5 feet and northerly winds from the N to NE 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 by
.PREV DISCUSSION... /issued 353 AM AST Wed Mar 29 2017/
SYNOPSIS...A surface high across the southwest Atlantic will
push the surface low to the northeast of the region further
northeast well away from the local islands. As this happens, the
local winds will shift to the north northeast today. Lingering
moisture across the region will combine with local effects to
induce the development of showers and possible thunderstorms along
and south of Cordillera Central today. Winds are expected to
become more easterly by the weekend as the surface high drift
eastward while weakening. North swell is expected to affect the
local waters late Wednesday and Thursday.
SHORT TERM...Today through Friday...
Partly cloudy skies prevailed across the local islands overnight.
Some light passing showers were seen across the Caribbean coastal
waters. Local Area remains under the influence of a surface low
pressure system which was located several hundred miles northeast of
the area. Trailing moisture associated with this feature will
continue to aid in the development of showers and possible
thunderstorms mainly over the Cordillera Central of Puerto Rico. The
difference today it is that the wind has shifted northerly. As a
result,shower activity will be focus mainly over the southern slopes
of Puerto Rico.
As the aformentioned area of low pressure continue to move away from
the area, a drier airmass is expected to encompass the region
Thursday and Friday as a high pressure system builds across the
LONG TERM...Saturday through Wednesday...
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
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...Mainly VFR conditions are expected to prevail across all
TAF sites through at least 29/16z. Periods of MVFR conditions can be
expected across TJPS and TJMZ between 29/16z through 29/22z in SHRA.
Low level winds will be mainly north and northwest at 10 kts or
MARINE...Seas of 3 to 5 feet will continue to prevail across
the Atlantic waters, with seas 2 to 4 feet across the Caribbean
waters. A moderate risk of rip current will continue across the
Atlantic shoreline of Puerto Rico today and tonight. A northerly
swell will arrive across the local waters late Wednesday into
Thursday with seas increasing up to 6 feet.
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 75 84 74 / 20 30 30 10
STT 84 74 85 73 / 40 30 30 20