336
FXCA62 TJSJ 180826
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
426 AM AST Fri Oct 18 2024

.SYNOPSIS...
A tropical wave, Invest 94L will move north of the area today and
tonight, increasing the potential for showers and thunderstorms.
Conditions will become more favorable for rainfall activity for
the weekend and next week, with an elevated risk of flooding
anticipated. A northerly swell will increase the risk of rip
currents to high for Monday.

&&

.SHORT TERM...Today through Sunday...

Overnight shower activity has gradually increased over the waters
under easterly winds. Some showers moved inland over areas that
include northeastern Puerto Rico (including sectors of the
metropolitan area), southeastern Puerto Rico, Vieques, and the USVI.
Stations reported minimum temperatures in the upper 70s to low 80s
across lower elevations of the islands, and in the upper 60s to low
70s across higher elevations of Puerto Rico. Current satellite
derived precipitable water (PWAT) values, indicate a contrast
between a drier patch with values around 1.10 to 1.30, over most of
Puerto Rico and its northwestern and western waters, and the
moisture field related to a tropical wave, Invest 94L, with values
above 2.00 inches, thats currently east of the U.S. Virgin Islands.
According to the latest tropical weather outlook: Invest 94L has a
low formation chance (10 percent) through the next 7 days. However,
it is still producing disorganized showers and thunderstorms east
and northeast of our local islands. The system will quickly move W
to WNW, passing near or just north of the area today, increasing
moisture and instability as well as increasing the potential for
showers and t-storms. An elevated risk of flooding, river rises, and
mudslides is forecast. The moisture field of above 2 inches, related
to this system will engulf most of the region today through this
evening. A lull in the wet period during the short and long term
will occur as a drier air patch moves across the area after Invest
94L during the overnight hours on Saturday. PWAT values will
increase again, to above 2.0 inches Saturday afternoon through
Sunday as both moisture reaches the area from the east and a frontal
boundary, with a pre-frontal trough, also digs to just north of the
Central Caribbean by Sunday. With elevated flooding risks during the
short term period, flooding of urban areas, roads, small streams and
are forecast with isolated flash flooding possible.

.LONG TERM...Monday through Friday...
A mid to upper trough will continue to escort a cold front just
to the northwest of the islands. At the surface, high pressure
over the eastern Atlantic will drive the trade winds from the
southeast on Monday. By Tuesday and Wednesday, another mid to
upper level trough will exit the eastern coast of the United
States, causing the winds to gain a more southerly direction from
the surface into the middle levels of the atmosphere. Under this
flow, moisture will move from the Caribbean Sea into the local
islands, increasing the potential for showers and thunderstorms.
The first pulse of moisture is anticipated for late Monday into
Tuesday, and there could be a break on Wednesday. By the end of
the week, however, additional areas of moisture will reach the
islands. With southerly winds, available moisture will combine
with local effects to trigger showers along the Cordillera
Central, then moving across northern Puerto Rico. Additional
activity is also expected in the local waters, reaching the Virgin
Islands, southern and eastern Puerto Rico at times too.

&&

.AVIATION...
(06Z TAFS)

E to ESE winds up to 11-15 kts with sea breeze variations and higher
gusts, decreasing and with land breeze variations after 18/22Z.
SHRA/TSRA over the waters, increasing after 18/09Z, can reach
JSJ/ISX/IST and promote MVFR conditions. MVFR conditions can also
result from VCSH/VCTS starting over the interior and moving towards,
and affecting, TJBQ (and possibly TJPS) around 18/17Z-22Z.

&&

.MARINE...
Invest 94L located east of the Leeward Islands will pass just north
of the region today. This will bring squally weather across the
local waters from through tonight, particularly across the Anegada
Passage and the Atlantic waters. By early next week, swells from a
low pressure over the western Atlantic will spread across the
Atlantic waters and passages.

&&

.BEACH FORECAST...
A small long-period northeasterly swell will contribute to a
moderate rip current risk along northern Puerto Rico, Culebra and
Saint Croix. This risk will persist through the weekend,
potentially increasing to high on Monday as another northerly
swell arrives.

&&

.HYDROLOGY...
Conditions will shift to the wet side starting today. First,
Invest 94L will bring increasing showers and thunderstorms across
the area. Then, for the weekend and next week, an approaching cold
front and moisture coming from the Caribbean Sea will combine to
generate additional periods of rain. This will increase the risk
of flooding, mudslides and rapid river raises.

&&

.CLIMATE...
The hot streak of consecutive days above 90 degrees could continue
today, unless enough showers and cloudiness prevent temperature
readings to reach this threshold. Regardless, 39 days of highs
above 90s have been recorded already at the Primary Climate Site,
located in the LMM International Airport.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...MRR
LONG TERM....ERG

NWS SJU Office Area Forecast Discussion