Special Weather Statement, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Melbourne FL
1122 AM AST Tue Mar 9 2021

.UPDATE...
Partly cloudy skies prevailed over land areas this morning with
scattered showers crossing the coastal waters and a few light
showers pushing through the eastern PR. Forecast looks on track,
with no significant changes made. The mid to upper level ridge
continues to hold across the region today, and is expected to
gradually erode over the next few days. The 12Z sounding for TJSJ
shows a significant dry layer starting around 750mb level, however
the precipitable water was 1.20 inches. Some locally induced
afternoon showers over much of the local area today, mainly over
central interior and west sections of PR and mainly on the west-end
or just downwind of the remaining Islands including the U.S. Virgin
Islands.

&&

.AVIATION...
VFR conditions through the TAF period. Brief VCSH ongoing across
portions of PR and remaining Islands, mainly affecting TJSJ and
IST/ISX. No significant hazards are expected across the local
terminals through the TAF period. Winds are ENE and have increased
to 10-15 KT with gusts 20-25 KT possible late this morning and
are expected to stay steady through the rest of the day. Sea
breeze variations are expected today. VCSH possible late this
afternoon and early evening for ISX/NCM/KPK and JSJ.

&&

.MARINE...
Sea conditions remain hazardous for the offshore Atlantic waters and
will expand tonight and Wednesday towards the Mona and Anegada
Passages. Buoy 41043 reported this morning seas of 8-9 ft with an
increasing swell from the north. This swell is forecast to continue
to increase to a period of 9-10 seconds tonight into Wednesday.
The Small Craft Advisory is already in effect for the Atlantic
offshore waters and will get in effect for the nearshore Atlantic
and Mona Passage tonight followed by the waters west of NW Puerto
Rico and around Culebra, Vieques and St Thomas late tonight.

Due to this increasing swell, the High Risk for Rip Currents will
continue for the northern coasts of PR and northern islands and the
risk will reach the corners of the island by tonight into
Wednesday.

&&

.PREV DISCUSSION... /issued 452 AM AST Tue Mar 9 2021/

SYNOPSIS...

Relatively fair and stable weather conditions with isolated
showers will prevail today. The proximity of a frontal boundary
will increase moisture content tomorrow through Thursday. Late
this week into the weekend looks unsettled as an upper-level
trough moves near the area and further increases instability and
moisture content. A northerly swell will cause hazardous seas
starting today.

SHORT TERM...Today through Thursday...

A surface high pressure is entering the western Atlantic, and a cold
front just northwest of the local islands will remain offshore and
it is not expected to directly impact the local islands today.
However, the frontal boundary will get sheared off and will
fragment by Wednesday, which will cause moisture to increase on
Wednesday into Thursday. The surface high pressure that is
entering into the western Atlantic will cause ENE winds today as
it tightens the pressure gradient, causing stronger winds this
afternoon and tonight into Wednesday. In the mid to upper levels,
a trough will approach the local area for Thursday, which will
enhance the chances for isolated thunderstorms on Thursday
afternoon over western PR. As far as temperatures go, near normal
temps are expected, with high temps in the mid 80s across the
lower elevations.

For today, the sfc high pressure will gradually tighten the pressure
gradient, causing ENE winds up to around 20 mph. This will result in
brief trade wind showers once again in the morning, affecting mainly
the USVI and eastern PR. That said, in the afternoon, the hi-res
model guidance suggests that showers will affect the eastern and
southern coastal municipalities, but past the mid-afternoon hours, a
few showers could also affect the eastern to western interior
sections of Puerto Rico, though accumulations are not expected to
cause significant hazards due to sfc-3km mean wind being nearly 20
knots according to the forecast soundings. That said, the global
models do not share this rainfall solution, but given the recent
model performance, we gave some consideration to the hi-res models,
though toned down the total amount of rain.

For Wednesday and Thursday, the frontal boundary to our northwest
could start getting sheared, losing definition and will become
fragmented. This will cause higher moisture to move into the local
waters and western PR by Wednesday afternoon and Thursday. This
could then cause shower activity across western PR in the afternoon
Wednesday , and widely scattered showers over the local Atlantic
waters during the night. By Thursday, a trough in the mid and upper
levels may cause some instability in the local area, and isolated
thunderstorms were added to the forecast for Thursday afternoon
across western PR.

LONG TERM...Friday through Tuesday...

According to model guidance weather conditions will become wetter by
the end of the workweek through the weekend. An old frontal boundary
and an easterly disturbance will continue maintaining a high
moisture content at lower levels over the forecast area on Friday.
GFS suggests precipitable water content increasing up to 1.5
inches through at least late Saturday night. In addition, weather
conditions aloft will become conducive for convective development
as the divergent side of a building polar trough settles over
Puerto Rico and U.S. Virgin Islands early Friday through at least
Sunday. In the meantime, a mid level short wave trough over the
central Atlantic will move southward and settle over the local
area on Friday before exiting the area late Sunday night. This
will set a colder air pattern aloft with 500 mb temperatures
cooling to -12 degrees Celsius between Friday and late Saturday
night.

This combination will produce an increase in areal coverage of
shower activity. The instability and diurnal heating could
support isolated thunderstorm development across the outer
Atlantic Waters and, with an east southeasterly wind flow,
portions of northwestern Puerto Rico between Friday and late
Saturday night. However, latest GFS shows the presence of drier
air within the 850-700 mb layer that could suppress convection and
possibly limit shower activity. Nevertheless, even with the
presence of this layer of drier air, models are in agreement that
environmental conditions will be somewhat favorable to support
enhanced shower activity by the end of the workweek into the
upcoming weekend. Showers that develop could cause urban and small
stream flooding and ponding of water on roadways. By Sunday and
early next week, the mid short wave trough and polar trough are
expected to move eastward as a mid to upper level ridge is
forecast to move in from the west. This will re-establish the
trade wind cap with weather conditions improving through the long
term forecast.

AVIATION...VFR conditions to prevail through the forecast period.
Brief VCSH could affect the IST/ISX and JSJ terminals this morning.
However, no significant hazards are expected across the local
terminals. Light and variable winds through 09/14Z, increasing to 10
to 15 knots and gusty from the ENE thereafter with sea breeze
variations. VCSH possible at TJPS after 09/16Z.

MARINE...

A northerly swell will move across the Atlantic waters and spread
into the local waters and passages today. Therefore, choppy and
hazardous marine conditions will continue across most of the local
waters, with seas between 5 to 10 feet and winds up to 20 knots
from the E-NE. Small craft advisory is in effect starting today for
most of the local waters. A high risk of rip current will come
into effect today for all the northern coast of Puerto Rico,
Culebra and St. Thomas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  84  74  85  74 /  30  30  30  30
STT  84  74  83  73 /  30  30  30  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from 6 PM AST this evening through late
     Wednesday night for Culebra-Mayaguez and Vicinity-Northeast-
     Southeast.

     High Rip Current Risk through late Wednesday night for North
     Central-Northwest-San Juan and Vicinity.

VI...High Rip Current Risk from 6 PM AST this evening through late
     Wednesday night for St.Thomas...St. John...and Adjacent
     Islands.

AM...Small Craft Advisory from 8 PM this evening to 2 PM AST Thursday
     for Anegada Passage Southward to 17N-Coastal Waters of
     Northern Puerto Rico out 10 NM-Mona Passage Southward to
     17N.

     Small Craft Advisory until 2 PM AST Thursday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N.

     Small Craft Advisory from 2 AM Wednesday to 2 PM AST Thursday
     for Coastal Waters of Northern USVI and Culebra out 10 NM-
     Coastal Waters of Northwestern Puerto Rico out 10 NM-
     Coastal Waters of Southern USVI Vieques and Eastern Puerto
     Rico out 10 NM.

&&

Watson/Negron/Haley/Kelly

Perspectivas sobre Condiciones Peligrosas del Tiempo
Servicio Nacional de Meteorologia en San Juan PR
437 AM AST martes 9 de marzo de 2021

AMZ710>745-PRZ001>013-101000-
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-
437 AM AST martes 9 de marzo 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

.Viento...Se esperan vientos sostenidos en exceso de 20 mph (17
nudos) a traves de las aguas locales.

.Oleaje...Se espera oleaje peligroso de hasta 8 pies a traves de las
aguas del Atlantico y pasajes locales.

.Corrientes Marinas...Existe un riesgo alto de corrientes
marinas para las playas del norte de Puerto Rico en el dia de hoy,
pero comenzando esta noche, todas las playas desde el noroeste hasta
el noreste de Puerto Rico y Culebra tendran un riesgo alto de
corrientes marinas. Habra un riesgo moderado de corrientes marinas
para las playas restantes de Puerto Rico y Vieques para esta
noche.

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

El oleaje continuara peligroso el miercoles hasta por lo menos al
final de la semana. Advertencias para embarcaciones pequenas
continuaran estando en efecto por los proximos dias. Habra un riesgo
alto de corrientes marinas para el resto de la semana.

.Comunicado sobre informacion reportada por observadores...

No se espera activacion amplia de observadores. 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-VIZ001-002-101000-
San Tomas, San John e Islas Adyacentes-
Santa Cruz-Aguas cercanas del Atlantico y aguas
costeras adyacentes del Caribe-
437 AM AST martes 9 de marzo 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

.Viento...Se esperan vientos sostenidos en exceso de 20 mph (17
nudos) a traves de las aguas locales.

.Oleaje...Se espera oleaje peligroso de hasta 8 pies a traves de las
aguas del Atlantico y pasajes locales.

.Corrientes Marinas...Existe un riesgo moderado de corrientes
marinas para todas las playas rodeando las Islas Virgenes
Estadounidenses en el dia de hoy. Sin embargo, comenzando temprano
esta noche, tambien habra un riesgo alto de corrientes marinas para
las playas del oeste de San Thomas.

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

El oleaje continuara peligroso el miercoles hasta por lo menos al
final de la semana. Advertencias para embarcaciones pequenas
continuaran estando en efecto por los proximos dias. Habra un riesgo
alto de corrientes marinas para el resto de la semana.

.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.