National Weather Service San Juan PR
413 AM AST Fri May 10 2019
.SYNOPSIS...An unstable weather pattern is expected through the
weekend as the combination of a mid to upper-level trough and
deeper moisture will result in an increase in the coverage and
intensity of showers and thunderstorms. Conditions will improve by
early next week as a ridge builds aloft, resulting in less shower
activity across the area.
&&
.SHORT TERM...Today through Sunday...
A light to moderate east to southeast low-level winds will prevail
today becoming more southeasterly Saturday through Sunday due to the
passage of weakly induced low level trough and a tropical wave
moving westward across the eastern Caribbean. An amplifying mid to
upper-level trough and the associated subtropical jet will also move
across the southwestern Atlantic today through the weekend and
continue to erode the upper level ridge. This will weaken the trade
wind cap inversion while increasing layered moisture content/cloud
cover.
The combination of these features during the period will favor
strong low level moisture convergence/pooling across the region
along with increasing upper level divergence and instability. This
will therefore increase potential for shower development across the
islands and regional waters during the entire period. Early morning
showers will continue to stream westward while affecting portions of
the north and east coastal areas of the islands. Afternoon shower
development will follow mainly over the central interior, and
northwestern sections of Puerto Rico; as well as over the eastern
interior and parts of the San Juan metro where isolated to scattered
showers will be likely in the form of streamers steered by the east
southeast wind flow. Isolated afternoon showers can also be expected
to develop on the west end and downwind of the U.S. Virgin Islands
each day.
The anticipated periods of locally heavy rains during the afternoons
will cause ponding of water on roadways at times and may lead to
urban and small stream flooding in some areas today and over the
weekend. Current model guidance still maintain high precipitable
water values up to near 2.0 inches through the period. However, The
best potential for increased and enhanced convective development
still looks like late Saturday through Sunday but overall a moist
and unstable weather pattern is in store for the entire period.
.LONG TERM...Monday through Friday...
Conditions will improve by early next week as the upper-level
trough pulls away and a ridge aloft builds overhead. This will
result in a decrease in shower activity across the area. However,
enough moisture will still be present to result in some passing
showers across eastern portions of PR and the USVI during the
overnight and morning hours followed by more enhanced showers
across interior and western portions of Puerto Rico during the
afternoon hours due to daytime heating and local effects.
Isolated thunderstorms are also possible with the afternoon
activity given that there will be sufficient moisture in the mid-
levels and 500 mb temperatures will range between -7 and
-8 degrees Celsius, allowing for enough instability aloft to be
present. This ridging pattern is expected to hold through the end
of the work week.
&&
.AVIATION...Prevailing VFR cond durg prd. SHRA en route btw local
islands and ovr the coastal waters...SCT ocnly BKN lyrs nr FL022...
FL050...FL090...FL250. Mtn top obscr ovr Ern PR low cld lyrs/-SHRA
til 10/14Z. SHRA psbl nr TJSJ/TJMZ/TJBQ with brief MVFR low cigs
and SHRA btw 10/17Z-10/22Z. Sfc wnds bcmg fm E 10-15 kt with ocnl
higher gusts and sea breeze variations aft 10/14z. L/lvl wnds fm E-
SE 10-20 kt blo FL100. FEW tops btw FL100-FL150.
&&
.MARINE...Fairly tranquil seas between 3 and 5 feet will prevail
across the regional waters today and through the upcoming
weekend. Seas will become choppy by early next week as a larger
northerly swell arrives and spreads across the regional waters.
For beachgoers, a small northerly swell currently affecting the
area will result in a high risk of rip currents for the beaches
located along the north-central coast of Puerto Rico as well as
the San Juan and Vicinity coast. A low to moderate risk of rip
currents is expected elsewhere.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 87 77 88 76 / 50 30 50 50
STT 86 77 85 77 / 30 50 60 60