Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 311812
Area Forecast Discussion
National Weather Service San Juan PR
212 PM AST TUE MAY 31 2016
.SYNOPSIS...Showers and thunderstorms will continue through
Thursday with some localized flooding then taper off to nearly
nothing by Sunday as drier air enters the area beginning Friday.
At upper levels...a ridge extends north from the U.S.
Virgin Islands. At our latitudes this ridge retrogresses west
across Puerto Rico Thursday morning with high pressure continuing
over the western and central Caribbean Sea until it builds north
over the southern Bahama islands next Tuesday.
At mid levels...High pressure over the tropical Atlantic extends
over the southern Caribbean Sea. High pressure will continue there
and build northeast of the forecast area through Friday. High
pressure continues over the Greater Antilles through much of next
At lower levels...Moderate high pressure continues over the
central Atlantic through Sunday generating east southeast trade
winds over the local area. The high will retreat to the east
northeast but the flow will continue. Drier air with some Saharan
dust will enter the area early Friday and increase through Sunday.
.DISCUSSION...Strong showers and thunderstorms with frequent
lightning launched over the area early in the afternoon after
light passing showers this morning. More showers are now entering
Puerto Rico from the southeast and heavy rain is growing over east
central Puerto Rico in air with close to two and one quarter
inches of precipitable water. The Galvez-Davison Index will
increase this afternoon and tonight while an area of moderate
divergence aloft moves across the U.S. Virgin Islands to Puerto
Rico. Moisture is expected to continue at similar levels through
Thursday evening according to the GFS precipitable water
depiction. This will allow periods of urban and small stream
flooding to occur for the next several days most of which will
occur during the afternoons and early evenings. Tonight`s
thunderstorms are expected to remain active over the local waters
until late tonight.
On Friday drier air carrying Saharan dust will move into the area
and begin to choke off most of the convection which will be slight
by Sunday according to current solutions. Driest air is now shown
to occur Monday morning with about 1.3 inches of precipitable
water. A tropical wave that passes mainly south of the area will
allow us to regain some of the moisture we currently have by mid
week next week.
.AVIATION...SHRA and TSRA will continue to affect the flying area
through tonight. Although most of the SHRA and TSRA will remain over
water...some passing SHRA could reach TJSJ and the USVI terminals
the rest of the afternoon and this evening...resulting in brief MVFR
CIGS. SFC Winds from the ESE at around 10 to 15 knots with stronger
.MARINE...Winds and seas have increased over buoy 41043 which is
now running just a tad over 6.5 feet with winds around 18 knots.
Winds and seas over the local area except for the local near
shore waters are running somewhat below this. Local winds and
seas will increase through Thursday and the risk of rip currents
will also become high by Thursday in the current forecast.
Conditions begin to improve after Friday. At this time small craft
advisories are not anticipated but seas will be close to 7 feet in
the northern outer waters and the Anegada passage until Friday.
.PRELIMINARY POINT TEMPS/POPS...
SJU 77 87 76 87 / 60 60 40 40
STT 78 86 78 82 / 60 60 40 40