National Weather Service San Juan PR
521 AM AST Mon Apr 30 2018
.SYNOPSIS...Drier air will continue for one more day then a weak
trough will increase showers and bring a few thunderstorms across
the area. Although Wednesday will be almost as dry as today, the
period Thursday through Saturday will see a considerable increase
in moisture showers and thunderstorms for the area and flow will
become more southeast, and even southerly at lower levels above
the surface.
&&
.SHORT TERM...Today through Wednesday...
Clear to partly cloudy skies prevailed across Puerto Rico and the
U.S. Virgin Islands overnight. Some showers moved across the eastern
half of Puerto Rico and across the coastal waters. This activity was
associated with a patch of low level moisture embedded in the wind
flow which affected the local area. For this morning, some passing
showers are expected to affect the local islands from time to time.
Significant rainfall accumulation is not expected with this
activity. For this afternoon, some cloudiness with scattered showers
are expected to develop across the western interior and northwest
sections of Puerto Rico.
For Tuesday, moisture will increase from the east, enhancing the
development of showers and thunderstorms across the region, mainly
across the Cordillera Central of Puerto Rico. After this patch of
moisture, a slot of dry air is expected to encompass the region on
Wednesday. An upper level ridge is expected to continue dominating
the local region next couple of days. This will result in relatively
good weather conditions across the region, with most of the area
receiving little rainfall activity.
.LONG TERM...Thursday through Monday...
An upper level low north of the area will dig southeast and
displace the ridge to the east Thursday and Friday. This will
send a jet from the southwest across the area, but the present GFS
is suggesting that considerable convergence aloft will work
against deep rising motion. Nevertheless, the passage of a low
level trough through the area Wednesday night will bring moisture
up from the southeast and with it rising motion in the lower
levels. This moisture and upward motion will arrive in several
bands that will almost assure that showers and a few
thunderstorms will develop over many areas Thursday through
Saturday. On Sunday most of the good convection will have moved to
the east, but residual moisture and heating will allow showers to
flare again. A minor surge of moisture on Monday will also bring
showers across Puerto Rico with isolated to scattered showers
around the U.S. Virgin Islands. This period beginning Thursday
will mark a major transition from the typically drier March and
April to May, the second wettest month of the year--at least for
eastern Puerto Rico. If moisture holds and upper levels become
even a little more favorable it may also mark the beginning of
regular local urban and small stream flooding in the heaviest
showers.
&&
.AVIATION...VFR conditions will prevail across all TAF sites through
at least 30/16Z. Brief periods of MVFR conditions with mountain
obscurations can be expected across TJMZ and TJBQ from 30/17Z-
30/22Z. Low level winds will be mainly east southeast at 15 to 20
kts. Maximum winds WNW at FL410 at 30/18Z.
&&
.MARINE...Marine conditions remain somewhat relaxed, although
winds are generating choppy seas in the local Atlantic waters.
Small craft will need to exercise in AMZ710 and AMZ712. Small
craft advisories are not expected until Thursday when winds will
begin to generate 7 foot seas in the Atlantic. These will spread
into the Caribbean on Friday.
&&
.FIRE WEATHER...
.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 86 76 / 20 40 40 40
STT 82 77 85 77 / 20 40 40 40