Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 171705

Area Forecast Discussion
National Weather Service San Juan PR
105 PM AST Thu Oct 17 2019


Active weather is expected for the next several days as a tropical
waves moves through beginning tomorrow. Given the already saturated
soils from recent rains, there is a high probability for local
flooding across the region as heavy rains move through. Next week
looks a bit less active than the weekend, but should still be fairly
busy with scattered showers and thunderstorms.


.SHORT TERM...Tonight through Saturday...

Unsettled weather conditions are forecast across the local area
starting Friday through the weekend. Today locally and diurnal
induced showers and thunderstorms should diminish across the area by
sunset leaving partly cloudy skies, and variable and light easterly
winds. A tropical wave and its associated moisture will continue to
progress to the east through the overnight hours, and affect the
U.S. Virgin Islands, Culebra and Saint Thomas and Saint John`s early
Friday morning with showers and thunderstorms. This activity will
continue to move east, bringing showers and isolated
thunderstorms to eastern Puerto Rico and the interior, western,
and northwestern areas during the afternoon. Additionally, these
showers and thunderstorms will be enhanced as a result of diurnal
and local effects. Showers and thunderstorms that develop will
move slow as a result of a light low-level steering flow. This
will lead to urban and small stream flooding and mudslides in
steep terrain. Exacerbating the issue is soils remain saturated
from previous days rainfall and any additional rainfall will cause
flashy rivers from the interior, western and northwestern areas
of Puerto Rico on Friday trough the weekend.

Saturday, the TUTT low is forecast to cutoff to the south of Puerto
Rico and provide limited instability, however, the cutoff low and
the tropical wave will draw deep tropical moisture over Puerto Rico.
This will lead to the development of showers and thunderstorms
during the afternoon across most of Puerto Rico. This activity will
further the flooding threat across the interior and western areas of
Puerto Rico. Also, rainfall of 1 to 2 inches will cause flooding
conditions over the metro areas of Puerto Rico.

.LONG TERM...Sunday through Thursday...

After a few active days of weather in the short-term, weather
conditions will calm down a bit heading into next week. However,
there will still be the potential for showers and thunderstorms, as
well as urban and small stream flooding. Lingering moisture from the
tropical wave will still be in place for Sunday. Upper level
dynamics look minimally favorable for enhanced shower activity as
the upper tropospheric trough moves further southwest. Thus, Sunday
has the potential to see above average shower activity. Low level
steering flow looks to be at or above 10 knots, which should help
keep showers moving. Similar conditions will prevail for Monday.

By Tuesday, the forecast picture becomes a bit more uncertain. The
European model has another upper level trough moving just to our
west. This current forecast would definitely help to enhance showers
across the region for Tuesday. The European model then moves the low
quickly out of the area. However, the American model does not put
the low to our west till Wednesday, and has it meander in a similar
location into the weekend. Despite the uncertainty, it appears
fairly certain that the long term forecast will be wetter than
normal. Thunderstorms with gusty winds, frequent lightning, and
heavy rain are possible, with the potential for local flooding.
Lastly, no major Saharan dust events are anticipated for the next



TSRA/SHRA are expected to develop across over the
interior areas of PR, and terminals TJMZ and TJBQ by 17/15Z before
diminishing by 18/03Z. Elsewhere across PR eastern terminals
VCSH/SHRA are possible through 17/23Z. Light easterly winds of 10
kts are less will prevail through the forecast period.



Seas are quite calm, with wave heights below 5 feet across the
region. Similar conditions are expected for the next week. Winds
will remain out of the east up to 15 knots. The biggest threat
remains the possibility for showers and thunderstorms across local
waters. These showers have the potential for frequent lightning,
gusty winds, and heavy rain.


SJU  78  87  77  89 /  50  60  40  40
STT  79  88  82  87 /  60  60  40  40




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