National Weather Service San Juan PR
522 AM AST Fri May 31 2019
.SYNOPSIS...
A Flash Flood Watch is in effect for Puerto Rico and the U.S. Virgin
Islands until Friday Evening. The mid to upper-level trough will
continue to move away from the local islands through Saturday.
However, linger low- level moisture and instability will induce
showers and thunderstorms across the northern and interior areas of
Puerto Rico, as well as the U.S. Virgin Islands today. A slight
improvement in weather conditions is expected on Saturday.
However, showers and isolated thunderstorms are possible during
the afternoon through the middle of next week. Then another mid to
upper-level is forecast to develop north of Puerto Rico, and cause
unsettled weather late in the week into the weekend.
&&
.SHORT TERM...Today through Sunday...
A Flash Flood Watch remain in effect for Puerto Rico and the U.S.
Virgin Islands at least until later this evening.
The mid- to upper-level trough will linger across the northeastern
Caribbean through the period. However the trough will continue to
lift east northeast and slowly weaken, as a high pressure ridge
builds and spreads across the region from the west over the upcoming
weekend. In the meantime, a fairly moist east to southeast low level
wind flow will persist. The abundant tropical moisture and the
unstable conditions aloft will therefore continue to support a
moderate to high potential for shower and thunderstorm development
across the islands and coastal waters at least through today. Also,
due to the fact that the soils remain saturated, it would not take
much rainfall to trigger rapid river rises, urban and small stream
flooding as well as mudslides in areas of steep terrain. For this
reason the Flash Flood watch will remain in effect at least until
later this evening.
Later today and through Saturday, the present model guidance and
forecast calls for decreasing mid to upper level cloudiness with
breaks in cloud cover. This will also favor a better chance for
shower and thunderstorm development. This will result in periods
of heavy rains and cause urban and small stream flooding.
Although troughiness aloft is expected to weaken and low level
moisture convergence content will slightly decrease by Saturday and
Sunday; still expect periods of passing overnight and morning
showers over the coastal waters and portions of the east coastal
sections of the islands. This will be followed by afternoon
convection across the interior and western Puerto Rico Saturday
through Sunday.
&&
.LONG TERM...Monday through Saturday...
A digging mid to upper-level trough across the western Atlantic
will create weak troughiness north of Puerto Rico early next
week. The combination of modest low-level moisture, surface
heating, and weak instability will induce showers and isolated
thunderstorms during the afternoon across Puerto Rico and the U.S.
Virgin Islands. Also, showers are possible across portions of
eastern Puerto Rico and the U.S. Virgin Islands during the early
morning.
Thursday, a mid to upper-level trough is forecast to develop near
the Bahamas, and is expected to continue move to the southeast
through Saturday. The proximity of the trough to Puerto Rico will
increase upper-level instability during the afternoon mainly
across portions of western, interior and northern areas of Puerto
Rico. Additionally, a weak subtropical jet and modest low-level
moisture will also aid in the development of showers and isolated
thunderstorms over the aformentioned areas above through
Saturday. Elsewhere, isolated to scattered showers are forecast
during the afternoon.
&&
.AVIATION...
SHRA/ Isold TSRA likely across the flying with VCSH
at all TAF sites thru the fcst prd. As a result, brief periods of
MVFR conds will be possible in low CIG/SHRA. Isold TSRA psbl enroute
btw islands durg prd. SFC wnds LGT/VRB bcmg fm E-SE 10-15 kts with
ocnly hir gusts and sea breeze variations aft 31/14z.
&&
.MARINE...
Showers and thunderstorms will develop across the Caribbean and
Atlantic waters today. These thunderstorms will create choppy
marine conditions through the afternoon. Some thunderstorms
could produce winds up to 30 kts with higher gusts. Seas up to 5
feet across most the Caribbean waters. Elsewhere seas will range
from 2 to 4 feet. Winds will be out of the east to southeast at 10
to 15 kts. Today winds will be out of the east to southeast at 10
to 15 kts with higher gusts likely.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 86 77 / 50 40 40 30
STT 85 76 85 77 / 60 40 40 50