FXCA62 TJSJ 201850
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
250 PM AST Tue May 20 2025
.KEY MESSAGES...
* Southeasterly winds will lead to above-normal temperatures through
midweek, particularly in urban and coastal areas. There is a Heat
Advisory in effect through 5 PM for northern, western, and
southern PR. Another Heat Advisory will likely be issued on
Wednesday.
* An area of suspended Saharan dust will linger through midweek,
resulting in hazy skies.
* Diurnally induced afternoon showers and thunderstorms are
expected to develop each afternoon across portions of central,
western, and northern Puerto Rico through the workweek. Urban
and small stream flooding is expected with this activity.
&&
.SHORT TERM...Today through Thursday...
Sunny to partly cloudy skies prevailed across Puerto Rico and the
U.S. Virgin Islands today. Showers and isolated thunderstorms
developed during the late morning and early afternoon hours over
portions of north central Puerto Rico. As of 2 PM, the Doppler radar
estimated between 1.00 and 1.50 inches of rain in San Juan, Arecibo,
and Camuy. Maximum temperatures were from the upper 80s and low 90s
across the lower elevations of the islands, and from the upper 70s
to mid 80s across the higher mountains of Puerto Rico. The wind was
from the southeast up to 15 mph with sea breeze variations and
higher gusts across coastal areas.
The Azores high will continue to build into the northeastern
Caribbean through the period, while a weak surface trough lingers
northeast of the region. These features will promote light to
moderate southeasterly winds through at least Wednesday. Moisture
levels will remain at normal to slightly above normal levels, while
a weak SAL continues to slowly diminish over the area. Therefore,
warmer temperatures will persist through at least Wednesday, with
heat indices increasing between 108F-112F across urban areas and
lower elevations of the islands. Winds will acquire a more easterly
component and increase in wind speeds on Thursday, as a brief low-
level ridge builds over the western Atlantic and merges with the
broad Azores high. A small surge in low-level moisture will arrive
by midday on Thursday, aiding to the development of afternoon
showers and brief isolated thunderstorms over western PR. Across the
USVI, scattered showers will increase from the Atlantic waters and
the Anegada Passage by then.
.LONG TERM...Friday through Tuesday...
...From Prev Discussion Issued on May 20 at 519 AM AST...
The long-term forecast begins with weak ridging aloft which will
slightly reduce upper-level instability. Nevertheless, 500 mb
temperatures will remain between -6C and -7.5C, with 700–500 mb
and 850–700 mb lapse rates staying within climatological normal,
or even slightly steeper than usual. This will allow marginal
instability to persist through at least the weekend. The main
limiting factor will be moisture availability, as precipitable
water values and mid-level relative humidities fall to within
seasonal normals, occasionally dipping slightly below average.
Even so, moisture levels will remain sufficient for shower
development and afternoon convection, particularly when combined
with surface heating and local effects. However, this activity is
expected to have reduced areal coverage compared to recent days.
Additionally, breezy to windy conditions will prevail, promoting
fast-moving showers that will help limit rainfall accumulations
across the area. As a result, flooding risk will be mostly
limited, with the potential for ponding of water in roads and in
poorly drained areas. Localized urban flooding cannot be ruled
out.
The pattern begins to change by early next week as another upper-
level trough exits the eastern seaboard and deepens while moving
eastward toward the northeastern Caribbean. The forecast becomes
more complex, with model guidance suggesting that this trough may
interact with an approaching tropical wave, currently located near
25W. The combination of favorable upper-level dynamics and well-
above-normal tropical moisture could result in an elevated risk of
flooding. However, confidence in this scenario remains low, as it
lies near the end of the long-term forecast period. Changes in the
synoptic pattern over the coming days may affect the timing or
location of the area where these features converge. Therefore,
continue to monitor forecast updates closely as we move into early
next week.
&&
.AVIATION...
(18Z TAFs)
Brief MVFR conditions are possible thru 22z at TJBQ due to
diurnally induced SHRA/TSRA. The 20/12z TJSJ sounding indicated
ESE winds up to 17 kt blo 2000ft. HZ due to Saharan dust continues
but VSBY expected to remain P6SM, except in areas of SHRA/TSRA.
&&
.MARINE...
Light southeasterly winds will persist across most local waters
through at least Wednesday. A building surface high pressure over
the central Atlantic will bring moderate to locally fresh easterly
trades from midweek onward. Hazy skies will persist through at
least Wednesday in areas with limited shower activity due to the
presence of suspended Saharan dust. Isolated thunderstorms will
continue to develop across the regional waters, particularly
across the northern and western coastal waters of Puerto Rico each
afternoon.
&&
.BEACH FORECAST...
A low risk of rip currents is expected to continue through most of
the workweek. However, life-threatening rip currents can still occur
near jetties and piers.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-003-005-
007-008-010-011.
VI...None.
AM...None.
&&
$$
DSR/GRS