Rip Current in Puerto Rico, January 24, 2021

Area Forecast Discussion
National Weather Service San Juan PR
1207 PM AST Sun Jan 24 2021

.UPDATE...Patchy moisture has been forming along weak lines of
convergence along the old frontal boundaries stalling in the
area. One such boundary is 8 to 12 miles north of Puerto Rico.
Another stretches from the Leeward Islands to over and just south
of Saint Croix. Between these boundaries little rainfall is
occurring. At present these lines have been moving very little as
the flow is nearly parallel to them, however drier air behind the
lines just north of Puerto Rico is expected to invade the forecast
area from the north overnight and Monday. It is expected that
this will be followed by a more vigorous line that will invade the
outer Atlantic waters Monday night and Puerto Rico and the
northern U.S. Virgin Islands early Tuesday and continue for most
of the day.

The current sounding had similar moisture to 24 hours ago, but was
slightly drier than the sounding from last night. As has been the
case for a number of days, much drier air continues in the lower
levels above the marine layer, which today ends at around 7000
feet.

&&

.AVIATION...Although VFR conds will prevail at TAF sites, lcl MVFR
CIGs under narrow bands of clouds will persists around TISX and
TNCM. Aft 24/18Z there is a chc of -SHRA forming or mov ovr SWrn
PR and TKPK where mtn obscurations and periods of MVFR conds will
prevail. Conds imprvg aft 24/18Z but areas of MVFR conds to
return to the N coast of PR and TNCM aft 25/06Z. Sfc winds 10-15
kt in ENE flow with sea breezes, bcmg aft 24/23Z, less than 10 kt
in land breezes. Maximum winds NW 36-46 kt btwn FL430-480.

&&

.MARINE...No changes to the marine discussion. Model guidance
continue to indicate swell of 10 feet or more moving into the
forecast area on Saturday.

&&

.PREV DISCUSSION... /issued 430 AM AST Sun Jan 24 2021/

SYNOPSIS...Fair and stable weather conditions with limited
shower activity are expected through early next week. The
remnants of a weak cold front are forecast to linger across the
region Tuesday through Thursday, merging with the remnants of yet
another, but stronger frontal boundary by the end of the workweek
into the upcoming weekend, supporting a higher chance for
showers. Winds will remain light to moderate from the east to
northeast through Monday, increasing thereafter. Tranquil marine
conditions along with a moderate risk of rip currents will
continue today.

SHORT TERM...Today through Tuesday...

There is a weak area of high pressure at the surface north of the
local islands, which is causing light to moderate northeasterly
winds across the local area. For Monday and Tuesday, a stronger SFC
high pressure will be present across the southwestern Atlantic,
causing stronger northeasterly winds across the local islands.
Stable conditions are currently observed as a ridge dominated the
mid and upper levels. According to the latest forecast soundings,
near to below normal moisture are still expected over the local area
for the next few days, with the limited moisture available mainly
being in the lower levels. This combination of patterns is causing
mainly fair weather over Puerto Rico and the USVI, with only
isolated light showers occurring over the local waters during the
night and early morning hours. However, for today, the hi-res models
seem to be much more bullish in the rainfall forecast compared to
the global models, mainly due to the local effects and diurnal
heating over Puerto Rico. The NMM model was so bullish in the
afternoon rainfall over W-SW PR, that it was difficult to ignore and
thus scattered showers are in the forecast across central to the
southwestern quadrant of PR for this afternoon. The other hi-res
model, the ARW agrees with the NMM on the location of rain, but it
has less amount of rain in the solution.

As winds become stronger on Monday, the shower activity is expected
to be mainly isolated and brief through the day. There is only a
slight chance of rain on Monday afternoon, as the stronger NE winds
should reduce the chances of sea breeze convergence over the SW
portions of PR. Isolated and brief showers are forecast elsewhere in
the local area through the day on Monday. However, on Tuesday, the
remnants of a frontal boundary will be approaching the local area.
Cloudiness and rainfall as well as available moisture is expected to
increase. That said, the area with higher moisture and rainfall is
limited to a narrow band, which will move through the local area
during the day on Tuesday. At this time, it looks like there will be
an increase in shower activity, but the rainfall accumulations are
not looking like it would cause hazardous conditions more than some
ponding of water in poor drainage areas.

The daytime temps are expected to be near normal for the next few
days, with the lower elevations observing daytime temps in the low
to mid 80s and lows in the upper 60s to low 70s; while the higher
elevations will have high temps in the mid 70s to low 80s, and
overnight lows in the upper 50s to mid 60s.

LONG TERM...Wednesday through Sunday...

Model guidance continues to suggest that a relatively moist
weather pattern will dominate, particularly by the end of the
workweek into the weekend. A surface high pressure streaming
across the western Atlantic will push the remnants of an old
frontal boundary southward across the local islands into the
northeastern Caribbean on Wednesday into Thursday, promoting
periods of increased cloudiness and isolated to scattered shower
activity from time-to-time. As the aforementioned high moves away
into the north central Atlantic and a frontal boundary approaches
the region from the northwest, winds are to decrease and turn
from the east to southeast, trapping an area of near normal
moisture over the local islands through Friday. Further increase
in moisture is expected thereafter as the remnants of the
aforementioned frontal boundary move in along with the weakening
of the trade wind cap that results from the passage of a deep
polar trough. The combination of favorable conditions aloft with
above normal moisture, with model-estimated PW values ranging
from 1.5 inches on Friday morning to around 1.8 inches by Saturday
night, will support enhanced cloud coverage and prolonged shower
activity across the forecast area. Although it is too soon to
determine potential impacts, if this forecast materializes, we
could have the first rain event of the year.

AVIATION...VFR conditions expected across the local terminals for
the next 24 hours. Brief ISOL -SHRA is possible over the local
flying area this morning, which could cause light and brief VCSH.
VCSH possible at TJPS after 24/18Z as SCT SHRA develop over portions
of south and west PR. Light and VRB winds will be observed until
around 24/12Z, but NE winds and sea breeze variations at around 10
KT are expected thereafter until around 24/22Z. FEW to SCT SKY
expected today.

MARINE...Tranquil marine conditions with seas up to 5 feet are
expected today, turning choppy up to 6 feet for the outer
Atlantic waters tonight into Monday. Thereafter, another swell is
expected to invade the regional waters, generating choppy to
hazardous seas that may require the issuance of Small Craft
Advisories. Winds will remain light to moderate from the east to
northeast through Monday, increasing to 10-20 knots by Monday
night. There is a moderate risk of rip currents for beaches along
the north coast of Puerto Rico, all beaches in Culebra, eastern
beaches of Vieques, north beaches of San Thomas and northwestern
beaches of Saint Croix.

FIRE WEATHER...Drier air will continue to move into the region,
limiting any chance for wetting rains and causing relative
humidity to drop into the mid 40s to near 50 percent, while
promoting further deterioration of soils and fuel moisture across
the southern coastal plains of Puerto Rico. Although winds are
expected to remain generally light, sea breeze variations will
cause winds to peak around 15 mph between the late morning and
early afternoon hours. Both KBDI and 10-Hour Fuel Moisture values
at Camp Santiago have reached already elevated thresholds during
the previous day with 558 and 8 percent, respectively. Based in
the expected weather conditions and recent drying pattern, a Fire
Danger Statement has been issued for elevated fire danger conditions
expected across the southern coastal plains of Puerto Rico today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  83  73  83  73 /  10  40  30  70
STT  83  73  83  72 /  20  20  20  30

&&

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

SHORT TERM...WS
LONG TERM....CS
PUBLIC DESK...99

Perspectivas sobre Condiciones Peligrosas del Tiempo
Servicio Nacional de Meteorologia en San Juan PR
452 AM AST domingo 24 de enero de 2021

AMZ710>745-PRZ001>013-251000-
San Juan y Vecindad-Noreste-Sureste-
Este Interior-Norte Central-Interior Central-Ponce y Vecindad-
Noroeste-Oeste Interior-Mayaguez y Vecindad-Suroeste-Culebra-Vieques-
Las aguas costeras cercanas y lejanas a la costa del Atlantico y
Caribe-
452 AM AST domingo 24 de enero de 2021

Esta perspectiva sobre las condiciones peligrosas del tiempo es para
Puerto Rico y las aguas costeras del Atlantico.

.Dia Uno...Hoy y esta noche

.Corrientes Marinas...Existe un riesgo moderado de corrientes
marinas para playas del noroeste a noeste de Puerto Rico, las playas
de Culebra y las playas del norte y este de Vieques.

.Dias dos hasta el siete...lunes a sabado

El oleaje estara picado comenzando el lunes. Una marejada del norte
causara oleaje peligroso el lunes en la noche, permaneciendo
peligroso hasta el miercoles. Un riesgo moderado de corrientes
marinas es posible durante los proximos dias, pero se espera un
riesgo alto de corrientes marinas el lunes en la noche y el martes a
traves de la costa norte de Puerto Rico y la isla de Culebra.

.Comunicado sobre informacion reportada por observadores...

No se espera activacion amplia de observadores. Sin embargo, favor
de reportar cualquier informacion sobre vientos, oleaje y corrientes
marinas al Servicio Nacional de Meteorologia en San Juan mientras
siguen las indicaciones de las autoridades locales y estatales.

AMZ715-725-VIZ001-002-251000-
San Tomas, San John e Islas Adyacentes-
Santa Cruz-Aguas cercanas del Atlantico y aguas costeras adyacentes
del Caribe-
452 AM AST domingo 24 de enero de 2021

Esta perspectiva sobre las condiciones peligrosas del tiempo es para
Islas Virgenes Estadounidenses y las aguas costeras adyacentes.

.Dia Uno...Hoy y esta noche

.Corrientes Marinas...Existe un riesgo moderado de corrientes
marinas para algunas playas del noroeste de San Tomas y Santa Cruz.

.Dias dos hasta el siete...lunes a sabado

El oleaje estara picado comenzando el lunes. Una marejada del norte
causara oleaje peligroso el lunes en la noche, permaneciendo
peligroso hasta el miercoles. Se espera un riesgo moderado de
corrientes marinas durante los proximos dias, pero un riesgo alto de
corrientes marinas es posible el martes para playas de la costa
norte de San Tomas.

.Comunicado sobre informacion reportada por observadores...

No se espera activacion amplia de observadores. Sin embargo, favor
de reportar cualquier informacion sobre vientos, oleaje y corrientes
marinas al Servicio Nacional de Meteorologia en San Juan mientras
siguen las indicaciones de las autoridades locales y estatales.