National Weather Service San Juan PR
510 AM AST Sat Jun 23 2018
.SYNOPSIS...Moisture associated with a departing tropical wave
will continue to interact with an upper level trough northwest of
the area to result in cloudiness and periods of showers and
thunderstorms across the forecast area today. Weather conditions
are expected to improve early the upcoming work week.
&&
.SHORT TERM...Today through Monday...
Upper level trough interacting with low level moisture after
tropical wave passage resulted in thunderstorms and showers
developing over the Caribbean waters and the southern sections of
Puerto Rico. This activity is expected to continue to affect
sections of southern PR through the rest of the morning hours and
spread across the rest of the island through the day. Cloud cover
could delay afternoon convective development over the northwestern
quadrant of the island. Urban and small stream flooding is expected
with the heaviest showers as well as mudslides in areas of steep
terrain.
Moisture will quickly erode between Sunday through Monday. However
by Sunday afternoon, the available low level moisture will combine
with diurnal effects and result in showers with possible isolated
thunderstorms over western Puerto Rico. A surface high pressure just
northeast of the region will tighten the pressure gradient over the
islands and bring a trade wind surge. Saharan dust is expected to
return by Monday. Creating even drier conditions across the region.
.LONG TERM...Tuesday through Sunday...
Although an upper level trough across the central Atlantic is
expected to amplify into the north central and northeast Caribbean
through the forecast cycle; moisture will remain below the normal
range which will be the limiting factor for shower and thunder
development the upcoming week. At lower levels, a tropical wave
passage is expected late in the week with bulk of moisture remaining
south of the area. A surface high pressure across the central
Atlantic will yield fresh easterly winds much of the forecast
period.
If the long term forecast holds, expect a fair weather pattern
across the local islands with locally induced afternoon showers
and thunderstorms across western areas of Puerto Rico each day.
Under easterly winds, temperatures should remain near normal
values.
&&
.AVIATION...SHRA/TSRA are expected across the Puerto Rico terminals
through at least 22z. Early in the period mainly across the southern
terminals, then by 17z across the northern and western terminals.
Tempo MVFR conditions are expected with this activity as well as
SCT/BKN layers from FL025-FL150 and mtn obscd along the interior.
Across the USVI terminals, SHRA could move briefly at times. Low
level winds will continue ESE at 10-20 kts.
&&
.MARINE...A departing tropical wave will continue to result in numerous
showers and isolated thunderstorms across the local waters today,
particularly the Caribbean waters. A high pressure system in the
central Atlantic will move into the west-central Atlantic, tightening
the local pressure gradient and increasing the winds. This will
create hazardous seas Sunday into early the next work week. Seas 6
to 8 feet with occasional seas up to 10 feet by Sunday night
across the Caribbean waters.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 86 77 89 78 / 50 30 30 20
STT 86 79 88 79 / 50 40 40 20