Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 311525 AAA
Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
1125 AM AST TUE MAY 31 2016
.UPDATE...Dew points along coastal portions of Puerto Rico rose to
77 to 79 degrees during the morning have amended the dew point
grids to account for the greater moisture. This added to the heat
indices that were calculated. POP grids were also increased over
some waters and most land areas.
.DISCUSSION...Overall the 31/12z sounding came in very wet and fairly
unstable with a forecast parcel lifted index of minus 7. The
precipitable water was 2.20--slightly higher than yesterday`s 2.11
inches. Models all agree in high chances of showers and at least
scattered thunderstorms as the afternoon progresses, but they do
not agree on the extent of coverage. The situation, however, is
very similar to yesterday, except that there is more moisture
above 19 kft today. Therefore expect chances to be better over
northwest Puerto Rico for showers and thunderstorms. These could
start as early as noon, since showers are already in progress from
Villalba to Sabana Grande. Urban and small stream flooding are
likely in at least a few areas.
.AVIATION...SHRA and ISOLD TSRA expected over and north of
the Cordillera...pos affecting TJBQ/TJMZ and TJSJ. Winds from the
ESE at around 10 to 15 knots with stronger gusts.
.MARINE...Winds and seas will slowly rise across mainly the outer
waters. At this time small craft advisories are not expected.
.PREV DISCUSSION... /issued 817 AM AST TUE MAY 31 2016/
SYNOPSIS...A High pressure ridge north of the region and a broad
surface trough spread across the central and eastern
caribbean, will maintain a moist southeasterly wind flow across
the forecast area through most of the work week.
DISCUSSION...Scattered to numerous showers with thunderstorms
were observed across Puerto Rico overnight. Periods of very heavy
rainfall were observed--mainly over the southeast section of
Puerto Rico. Rainfall accumulations of between one to two inches
were recorded in some localized areas.
The combination of the upper trough just west of the region along
with a significant moist environment and local and diurnal
effects will continue to support rapid development of showers and
thunderstorm activity across portions of the islands and coastal
waters today and at least until Wednesday. Some of the showers and
thunderstorms will continue to produce periods of locally heavy
rainfall and gusty winds which will eventually lead to minor
flooding of urban areas, rivers and small streams, especially
along portions of the northern half of Puerto Rico, including
parts of the San Juan metro area. It is important to mention that
soils are saturated over the southeast, eastern interior and east
sections of Puerto Rico with recent periods of heavy rainfall.
Therefore, any additional rainfall, will result in rapid rises in
the rivers and creeks across these areas.
AVIATION...Mostly cloudy with VCSH across the eastern region during
the morning with brief periods of MVFR cond possible in and
around USVI terminals...TJSJ and TJPS. After 31/16Z...SHRA and
ISOLD TSRA are expected over and north of the Cordillera...
possibly affecting TJBQ/TJMZ and TJSJ. Winds will be ESE at around
10 to 15 knots.
MARINE...Winds are expected to increase across the coastal
waters--mainly in the Atlantic waters. As a result, small craft
should exercise caution as seas up to 6 feet and winds up to 15
knots are expected.
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 87 76 / 50 60 60 40
STT 87 78 86 78 / 40 60 60 40