Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 300032
Area Forecast Discussion
National Weather Service San Juan PR
832 PM AST Sat Apr 29 2017
.UPDATE...Numerous showers and thunderstorms developed during the
afternoon hours mostly along and north of Cordillera Central as
well as across the eastern sections of Puerto Rico. Radar
estimated between 2 to 3 inches of rain in several spots across
southeast and western sections of Puerto Rico during the afternoon
hours. Several Urban and Small Stream Advisories were issued for
numerous municipalities along eastern and western Puerto Rico.
Showers and thunderstorms diminished after sunset, however light
to moderate activity persisted during the evening across the
northern half of the islands as well as across the surrounding
waters. Some showers will continue to affect the region overnight.
For Sunday, a similar weather pattern is expected with showers in
the morning across windward areas followed by numerous afternoon
showers and isolated thunderstorms across western and interior
sections of Puerto Rico. weather conditions are expected to
improve slowly by Monday.
.AVIATION...An upper level trough will continue to produce
periods of SHRA across the Leewards and USVI taf sites overnight
and Sunday morning. SHRA/TSRA development expected after 30/16Z.
As a result periods of MVFR or even IFR conditions and mountain
obscurations expected at most of PR and USVI TAF sites. Low level
winds will continue mainly east at around 10 knots overnight,
increasing to 10-20 kts with higher gusts Sunday morning.
.MARINE...Mariners should exercise caution across most of the
local waters due to seas between 4 and 6 feet and winds between 15
and 20 knots. Thunderstorm formation is likely across the local
waters through at least Sunday.
.PREV DISCUSSION... /issued 446 PM AST Sat Apr 29 2017/
SYNOPSIS...The proximity of the TUTT and abundant amounts of low
level moisture transport across the forecast area will maintain
moist and unstable weather conditions through the weekend and into
early next week. Conditions will gradually improve by the middle of
next week, with a more seasonable weather pattern expected to prevail
by the end of the next week and into the following weekend.
SHORT TERM...Tonight through Tuesday...
Mostly cloudy and showery conditions prevailed across the entire
region today with showers and thunderstorms with areas of heavy rains
affecting several areas across Puerto Rico as well as the coastal waters
and U.S. Virgin Islands.
For the rest of evening hours expect variably cloudy conditions
to continue but shower activity should diminish over most land
areas. However by late night and early morning expect another
round of showers and thunderstorms to develop across the regional
waters. This activity should then stream west and northwest and
affect the east and south coastal sections of Puerto Rico and the
rest of the islands including the U.S. Virgin islands. The very
moist and unstable environment, will aid in further development of
showers and thunderstorms across the Cordillera Central of Puerto
Rico early in the afternoon, with the activity expected to spread
across the western interior and northwest sections of Puerto Rico.
periods of heavy rainfall will lead to urban and small stream flooding.
The upper level trough/Tutt is expected to linger just north and west
of the region enhancing the development of showers and thunderstorms
across the local area until at least Tuesday. Low level moisture transport
is also expected to remain high through this period with very unstable
conditions aloft. As a result, periods of enhanced showers and thunderstorms
can be expected to develop each afternoon across the Cordillera Central
of Puerto Rico and portions of the U.S. Virgin Islands.
LONG TERM...Wednesday through Sunday...
TUTT is expected to continue to linger north of the forecast area at
least until Wednesday. However as this feature continues to weaken
during, a mid to upper level ridge is forecast to build across the
forecast area from the west. The ridge aloft is then expected to hold
through the upcoming weekend allowing for less favorable conditions
for convective development. The surface high pressure across the central
Atlantic will also lift farther northeast by Wednesday therefore weakening
the local pressure gradient. This in turn will support a light to moderate
east to southeast trade wind flow through Sunday.
Expect periods of showers and isolated thunderstorms across the coastal
waters E Puerto Rico and the U.S. Virgin Islands during the late evening
and early morning hours followed by shower and thunderstorm development
mainly across the west and interior sections of Puerto Rico by late
morning and during the afternoon hours. As the ridge builds aloft and
moisture erodes during the latter part of next week a more seasonable
weather pattern is expected with near normal or slightly warmer temperatures
under the expected east to southeast wind flow.
AVIATION...A lingering trough will produce periods of +SHRA/TSRA at
times. SHRA/TSRA development expected til 29/23z, with BKN-OVC
Ceiling at FL025-FL100 are expected across the islands. As a result
periods of MVFR or even IFR conds and mountain obscurations at most
of PR and USVI TAF sites are expected the rest of this afternoon.
SHRA/TSRA formation expected across the regional waters and into the
USVI/E-PR aft 30/02z. Low level winds will continue mainly east at
10-20 kts with higher gusts til 29/23, dropping at 10 knots or less
MARINE... Mariners should exercise caution across the local waters
due to seas between 4 and 6 feet and winds between 15 and 20 knots.
Thunderstorm formation is likely across the local waters through at
.PRELIMINARY POINT TEMPS/POPS...
SJU 72 83 72 86 / 60 60 50 50
STT 72 81 72 87 / 50 50 50 50