Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 280144

Area Forecast Discussion
National Weather Service San Juan PR
944 PM AST Sat May 27 2017

.UPDATE...An isolated thunderstorm developed early in the evening
over Utuado and affected much of the interior and southwestern
municipalities of the island. Rainfall estimates were around one
inch of rain. During the afternoon hours, scattered to numerous
showers developed mainly over the western half of the island.
Several urban and small stream advisories were issued. The
doppler radar as well as raingages estimated between 2-3 inches of
rain with the heaviest showers. For the overnight hours into
Sunday morning, trade wind showers could move over land areas of
the USVI and eastern PR. Overnight temperatures are expected to
range between the low to mid 60s across the higher elevations to
the mid 70s across the coastal areas. No change from previous
forecast. Another round of afternoon convection is expected on
Sunday across the mountain ranges and western portions of PR.


.AVIATION...Mainly VFR expected to prevail overnight across all
terminals. However, trade wind showers are possible at times
across the Leeward/USVI/Eastern PR terminals. Resulting in mainly
VCSH and brief -RA with sct/bkn cigs at FL030. Latest TJSJ
sounding indicated ENE winds at 8-15 knots below FL100. TSRA
is expected to develop on Sunday afternoon across the interior
and NW quadrant of PR.


.MARINE...Buoys across the coastal waters of the islands were
indicating seas between 2-3 feet and northeast winds between
10 to 15 knots. Seas are expected to continue between 2 to 4 feet
through early next week. No change from previous discussion.


.PREV DISCUSSION... /issued 342 PM AST Sat May 27 2017/

SYNOPSIS...Mid to upper level trough with associated low pressure
area across the lesser antilles northeastward into the central
Atlantic will slowly drift westward through Sunday. A tropical
wave just east of the lesser antilles will approach the local area
Monday through Tuesday.

SHORT TERM...Tonight through Monday Night...Mid to upper trough
mentioned before will keep unstable conditions across the
northeast Caribbean through Monday. This, coupled with abundant
moisture and diurnal heating will result in an increased chance
for showers/thunderstorms across most of the area...especially
afternoons and early evening hours. On Monday night the leading
edge of a tropical wave currently east of the lesser antilles will
begin to impact the local islands. The interaction of the wave
with the mid/upper trough will result in a generalized increase in
showers/thunderstorms from east to west. Decided to increase the
chances for precipitation based on the expected interaction of the
two weather feature and the increase in available moisture.

LONG TERM...Tuesday through Sunday...The tropical wave will still
moving across the local area and so the chances for rain will
remain moderate to high with scattered showers and isolated
thunderstorms. Models indicate a slight decrease in the chances
for rain after Tuesday...however it looks like the environment
will remain rather moist and unstable as trofiness at mid/high
level remains across the eastern Caribbean.

AVIATION...SHRA expected through the USVI which will cause at
least VCSH across the TIST and TISX terminals this afternoon.
VCTS likely at the terminals in Puerto Rico this afternoon. Winds
from the E-ESE with sea breeze variations at around 15KT with
occasional gusts. SHRA activity to diminish after 27/23Z and winds
to diminish as well into the overnight hours, however, VCSH is
possible for TIST, TISX, and TJSJ in brief passing showers.

MARINE...Pleasant marine conditions should remain in place
through Tuesday with winds at or below 15 kts and seas at or below
5 feet. Locally higher winds and rough conditions in the vicinity
of showers and thunderstorms...especially Monday night through
Tuesday as the tropical wave moves through the coastal waters.


SJU  77  89  77  88 /  20  30  30  50
STT  78  88  78  87 /  20  30  40  60




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