Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 240913

Area Forecast Discussion
National Weather Service San Juan PR
513 AM AST Mon Jun 24 2019

Surface high pressure anchored across the west and central Atlantic
and a weak tropical wave moving across the eastern Caribbean, will
maintain moderate east to southeast wind flow across the region
today through Tuesday. Increasing moisture accompanying the tropical
wave along with local and diurnal effects will favor better potential
for shower development mainly over central and west portions of Puerto
Rico and parts of the San juan metro. The building anticyclonic flow
aloft will also provide sufficient ventilation for possible isolated
afternoon thunderstorm activity over the west interior and northwest
Puerto Rico.


.SHORT TERM...Today through Wednesday...

Upper level trough will continue across the western Caribbean
during the next few days, while upper level ridge builds over the
region. Moisture associated with a tropical wave will continue to
advance into the local area on Monday. This combined with local
effects will result in showers and isolated thunderstorms activity
mainly across the interior and northwestern Puerto Rico with
additional shower activity over portions of eastern Puerto Rico,
the U.S. Virgin Islands as well across the local waters. On Tuesday,
the bulk of the moisture will arrive to the islands, but the intensity
of the activity will be limited by the lack of upper level support.
However, once again, passing showers will be possible for the U.S.
Virgin Islands and eastern Puerto Rico followed by afternoon convection
along the interior and northwestern Puerto Rico. On Wednesday, a low
level perturbation will arrive into the area, aiding in the development
of afternoon showers across western Puerto Rico.

Temperature wise, southeast winds and upper level ridging will result
in heat indices near 105 degrees for the coastal municipalities of
Puerto Rico, as well as Vieques and St. Croix. This pattern will
continue at least until mid-week. Low concentration of Saharan dust
will continue until Tuesday, then a moderate layer will arrive on

.LONG TERM...Thursday through Tuesday...

By Thursday and at least into the following weekend, expect a
surface high pressure to remain anchored across the west and
central Atlantic. This will favor moderate east to southeast
winds across the region. Mid to upper level ridge will also hold
across the region through the end of the work week. However weak
pertubations in the easterlies will bring periods of shallow low
level moisture and passing showers across the area. This will
support isolated to scattered shower development over portions of
the islands or just off shore during the early morning; followed
by locally and diurnally induced afternoon showers mainly over the
west interior sections of Puerto Rico. Mostly fair weather skies
will prevail elsewhere during the afternoon hours. Another surge
of moderate concentrations of suspended saharan dust is also forecast
during the early part of the period.

By Saturday through Sunday another weak tropical wave is forecast to
enter and move across the eastern Caribbean. This may again bring
an increase in tropical moisture to the region. At this time
however model guidance continued to suggest that most of the
associated moisture accompanying the wave should remain south of
the area. In addition lack of good mid to upper level support
should limit enhanced early morning and afternoon convection
across the islands. The upper trough is forecast to retrograde
slightly westward toward the area but presently guidance continued
to suggest our area on the subsident side and therefore no widespread
or significant amount of rainfall is expected. Improving dry and
stable conditions with mostly sunny skies and generally a fair
weather pattern is so far forecast for Monday and Tuesday.


.AVIATION...HZ due to Saharan dust is expected to diminish across
the local flying area today. VFR conditions are expected to prevail
across all terminals. VCTS are expected for TJMZ/TJBQ after 24/16Z.
Surface winds will be out of the ESE at 10 to 20 knots at FL050.


.MARINE...Mariners can expect overall seas between 3 and 5 feet
across exposed waters and between 1 and 3 feet across protected
waters. Winds will continue from the east to southeast between 10
to 20 knots with occasionally higher gusts.

A moderate risk of rip currents will continue for some of the the
northern coast of Puerto Rico.


SJU  89  78  88  77 /  30  40  40  20
STT  90  80  87  78 /  30  40  40  20




LONG TERM....RAM is the U.S. government's official web portal to all federal, state and local government web resources and services.