National Weather Service San Juan PR
452 AM AST Sat Mar 31 2018
.SYNOPSIS...Below normal moisture is still expected through
Monday, which should limit the shower activity coverage and
intensity, so only isolated to light scattered showers are
expected through Monday. The local winds will remain from the NE
through the weekend, shifting to an easterly direction on Monday
and then SE by Tuesday and Wednesday as an induced SFC trough
moves in, bringing deep moisture. Upper trough will be over
Hispaniola on Tuesday and Wednesday, which should cause enough
instability for showers and thunderstorms over the local area.
&&
.SHORT TERM...Today through Monday...
Clear to partly cloudy skies prevailed across Puerto Rico and the
U.S. Virgin Islands overnight. Some showers were noted mainly
across the Atlantic waters. Local area remains under the influence
of an upper level ridge which is maintaining relative dry weather
conditions across the local area. The northeast wind flow will
transport patches of low level moisture from time to time today.
Showers will be focus mainly across the north and northeast
sections of Puerto Rico during the morning hours, followed by
afternoon convection to develop across the southwestern sections
of Puerto Rico.
For Sunday and Monday, a relatively dry air mass will encompass
the region, limiting the shower development. After Monday, an
induced surface trough will approach the local islands from the
southeast. As a result, increasing cloudiness with showers and
possible thunderstorms are expected thereafter.
.LONG TERM...Tuesday through Sunday...
The fair weather we have been enjoying and that we expect through
Monday may come to an abrupt end on Tuesday into Wednesday as an
induced SFC trough moves in, bringing plenty of deep moisture.
This trough will combine with the deep moisture and an upper
trough over Hispaniola, which will give us plenty of instability
to help sustain showers and thunderstorms over the local islands.
Locally heavy showers and some thunderstorms are very possible if
the model guidance were to verify and this weather pattern pans
out as it appears. At this time we kept the forecast as scattered
heavy showers with isolated thunderstorms for Tuesday and
Wednesday due to only moderate confidence that everything will
line up as the long range models indicate. Having said that, if
the models continue to show consistency in the forecast, the
forecast will likely reflect the higher confidence.
For Thursday, showers and thunderstorms are also possible, but
likely due to the combination of higher than normal moisture and
the local effects since the upper trough is expected to have
moved out of the local area. Then for the following weekend, at
this time it looks like locally induced showers and thunderstorms
are possible for Puerto Rico while only isolated showers for the
USVI since an upper ridge may be over the local area by then but
moisture will be near normal and it may combine with the local
effects and diurnal heating.
&&
.AVIATION...VFR conditions will prevail across the forecast area
through at least 31/22z. Some showers can be expected in the
vicinity of TJMZ this afternoon. Low level winds will be mainly
northeast at 10 to 15 kts.
&&
.MARINE...Seas continue to diminish and at this time we are
expecting seas of up to 6 feet. Winds will be up to 15 knots from
the NE today. There is still a high risk of rip currents from the
northwest to the northeast beaches of Puerto Rico today. Many of
the remaining beaches have a moderate risk of rip currents which
include eastern and western PR, Vieques and Culebra islands, the
eastern half of Saint Croix and the north and western beaches of
Saint Thomas.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 83 74 85 75 / 30 20 20 20
STT 84 71 84 72 / 20 20 20 20