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FXCA62 TJSJ 171753
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
153 PM AST Sun Aug 17 2025
.KEY MESSAGES...
* Hurricane Erin is still a powerful hurricane located about 200
miles north-northwest of San Juan, leading to southeasterly
winds and external feeder bands that are resulting in showers,
thunderstorms, and gusty winds.
* The Flash Flood Watch remains
in effect until Monday evening. Deteriorated marine and coastal
conditions remain, with seas up to 12 feet mostly in the
northwestern offshore Atlantic waters and the Mona Passage.
* Improving weather conditions are forecast for Tuesday with
limited coverage in shower activity and an increase in heat
indices along coastal and urban areas.
* For the U.S. Virgin Islands, another rainband is forecast for
lated this evening, resulting in periods of moderate showers.
&&
.SHORT TERM...Tonight through Tuesday...
Unsettled weather conditions prevailed during the morning hours as
external bands from Hurricane Erin moved over the islands. Winds
were predominantly from the southwest in the early morning hours,
leading to showers mainly across the southeastern section between
Salinas and Guayama. At 9:30 AM, showers and thunderstorms
increased across most of eastern Puerto Rico, spreading across the
island for the rest of the day, including the interior and western
interior sections. According to the NEXRAD Radar and surface
weather stations, gusty winds were observed with the strongest
showers, including 53 mph in Culebra and 49 mph in Charlotte
Amalie, St. Thomas. Across southeastern Puerto Rico, a gust of up
to 42 mph was reported in Las Mareas, Guayama, PR. Rainfall
accumulations were significant in municipalities near Adjuntas and
Salinas, with accumulations between 2 and 3 inches. Daytime
temperatures were much cooler today due to cloudiness and showers,
with temperatures remaining in the low to mid-80s.
The NHC bulletin located Hurricane Erin maximum sustained winds,
235 miles north-northwest of San Juan, PR. Although the system
continues its route to the western Atlantic, associated feeder
bands are expected to move over the U.S. Virgin Islands and
eastern sections of Puerto Rico this evening and into the late-
night hours. The strongest showers will continue to result in low-
level flooding, including at low- lying river crossings and in
small urban streams. Winds will become more southerly as the
system moves north. Given the expected conditions, the Flash Flood
Watch remains in effect until Monday evening.
For Monday, as Erin moves more northward into the Western Atlantic,
winds will be predominantly from the south. These surface winds
will drag tropical moisture with precipitable water values of 2.2
inches, as suggested by the global model guidance. These surface
conditions will lead to mostly cloudy skies and showers affecting
the southern coastal areas and, in the afternoon, the interior
mountain sections. According to the Glvez-Davison Index (GDI),
isolated thunderstorms are expected in most of the interior and
northern sections during the afternoon hours. The islands can
expect another wet day with an elevated chance of urban flooding,
exacerbating the currently affected areas. Therefore, we urge
residents and visitors to stay tuned to the weather updates for
the islands on Monday. For Tuesday, conditions will slightly
improve. Backing winds will bring the typical weather pattern to
the islands with a decent amount of moisture, again increasing the
heat threat. Additionally, a decrease in the available moisture
will limit the coverage of the showers during the afternoon hours.
.LONG TERM...Wednesday through Sunday... from previous discussion
issued at 500 AM AST Sun Aug 17 2025...
Some changes were introduced to the long-term forecast, particularly
for the upcoming weekend. Winds will mostly remain from the
southeast due to a surface high pressure lingering northeast of the
CWA. Model guidance suggests an upper-level low approaching the
local area by Wednesday morning, although the latest solutions agree
that this feature should move north of the region. Looking at the
mid-level temperatures, 500 mb temperatures drop to below
climatological normal on Wednesday, enhancing deep convection
activity. Due to PWAT values (1.6 - 1.8 inches), the likeliest
scenario would be an advective pattern with showers moving over the
U.S. Virgin Islands, Vieques, Culebra, and southeastern Puerto Rico
during the morning, while afternoon convection could develop over
interior and northwestern Puerto Rico. Rainfall accumulations could
lead to ponding of water over roadways, urban, and poorly drained
areas, with low chance of urban flooding along interior and
northwestern Puerto Rico. A drier air mass should filter into the
region by Thursday, and due to the presence of a mid- level ridge,
the shower activity may be limited.
As for the upcoming weekend, the National Hurricane Center is
currently monitoring an area of low pressure with a 0 % chance of
formation for the next 48 hours and a 20 % chance in the next 7
days. As mentioned in previous discussions, global model guidance
has been suggesting the potential for a vigorous tropical wave to
develop into a potential tropical cyclone approaching the Caribbean
Basin. Nevertheless, variability continues high, particularly on
Friday. Although the deterministic guidance from the GFS and ECMWF
agrees on an increase in moisture content, uncertainty remains high
regarding trajectory and intensity. Hence, the flooding risk will
remain limited for most portions of Puerto Rico and the U.S. Virgin
Islands, although it may change due to high uncertainty. Once again,
residents and visitors should keep monitoring and stay tuned to the
latest advisories of Hurricane Erin.
As mentioned in previous discussions, the heat risk is expected to
remain mostly limited to elevated across urban and coastal areas of
Puerto Rico and the U.S. Virgin Islands. Nevertheless, due to hotter
than normal temperatures and abundant moisture, the heat risk may
increase and become elevated to significant, meeting Heat
Advisory/Warning Criteria.
&&
.AVIATION...
(18Z)
Intermittent periods of SHRA/TSRA associated with Erin`s outer
rainbands are expected to continue over the local flying area
through at least Monday afternoon. This could cause tempo MVFR to
brief IFR conditions at times across the PR terminals thru 17/23z
and once again from 18/08z-22z. Across the USVI terminals, mainly
VFR conditions with periods of -RA/VCTS are expected to prevail.
However, tempo MVFR conds are possible btw 18/00z-08z. South winds
will prevail btw 10-20 kt with higher gusts at times.
&&
.MARINE...
Erin`s outer rainbands producing thunderstorms with torrential
rainfall and gusty winds will continue through at least Monday over
portions of the local waters. Swells from Erin will gradually
diminish from tonight through Monday morning, and Small Craft
Advisory conditions should improve across most waters, except in the
offshore Atlantic waters were the SCA could be extended through late
Monday due to seas up to 7 feet. Moderate to fresh southerly winds
will continue during the next 24-36 hours, becoming light to
moderate and from the east to southeast through midweek. A tropical
wave is expected to enter the eastern Caribbean on Friday,
increasing thunderstorm activity in general
&&
.BEACH FORECAST...
NO changes to the actual forecast. Life-threatening rip currents
and high surf conditions continue across the east, north, and
western facing beaches of the U.S. Virgin Islands and Puerto Rico
through early Monday. However, swells generated from Hurricane
Erin are likely to continue to impact the northern coastline of
the islands through the week.Dangerous swimming conditions will
persist across all coastlines through at least Monday.
Unexperienced surfers and swimmers are urged to avoid going into
the water.
Please refer to the latest Coastal Hazards Message (CFWSJU) and Surf
Zone Forecast (SRFSJU) for more information.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Flood Watch through Monday evening for PRZ001>013.
High Rip Current Risk through late tonight for PRZ001-002-005-
008-010-012-013.
High Surf Advisory until 6 AM AST Monday for PRZ001-002-005-008-
012-013.
VI...Flood Watch through Monday evening for VIZ001-002.
High Rip Current Risk through late tonight for VIZ001-002.
High Surf Advisory until 6 AM AST Monday for VIZ001-002.
&&
$$
SHORT TERM & KEY MESSAGES...LIS
LONG TERM & BEACH FORECAST....MNG
AVIATION & MARINE...DSR
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