Abundant low-level moisture in southerly flow resulted in areas of heavy showers across portions of the San Juan metro area.
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The episode as NWS SJU wrote it up.
Abundant low-level moisture in southerly flow resulted in areas of heavy showers across portions of the San Juan metro area.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Juan, PR wrote its last area forecast discussion before the first event at Sep 23, 10:04 AM AST, 4 hours 11 minutes earlier.
Area Forecast Discussion
National Weather Service San Juan PR
1004 AM AST Wed Sep 23 2020
.UPDATE...No changes were made to the overall weather or marine
forecast. The latest observations and guidance are still in
agreement with the ongoing forecast. As far as the hazards go,
the surf zone conditions are very dangerous and all inherited
advisories are still in effect. That is, Coastal Flood and High
Surf Advisories, continue in effect. In fact, we have received
reports of coastal flooding in some areas of northwestern Puerto
Rico. The breaking waves and overall conditions are expected to
become more hazardous this afternoon and evening compared to what
we have seen this morning, so if we were to make any changes to
the hazards, it would be to extend them. There is also the high
risk of rip currents across western and northern PR as well as
the USVI.
We are still expected thunderstorms this afternoon across the
northern half of PR and the northern USVI. Although high-res
model guidance is showing little in the way of rainfall, the
models have been underwhelming for the past few days, so there is
some uncertainty and therefore we went with more rainfall than the
guidance is suggesting. That said, the stationary front to the
north and west of PR is causing much cloudiness over the local
area, which may suppress some convection.
&&
.AVIATION...VFR cond expected through the forecast period. TSRA
expected near and around TJSJ and TJBQ this afternoon. TIST may
also observe VCSH in the afternoon. Light S-SE winds with sea
breeze variations through today.
&&
.MARINE...Dangerous marine conditions with seas up to 12 feet due
to a northerly swell. Small Craft Advisory in effect for most of
the local waters. Seas will remain hazardous through Friday.
&&
.PREV DISCUSSION... /issued 445 AM AST Wed Sep 23 2020/
SYNOPSIS...
A northerly swell is impacting the region through Friday, and
dangerous marine conditions are occurring. Please be very
cautious if at any northern facing beaches! More active weather is
expected for the next several days due to a stalled trough and
its associated moisture. Areas of isolated flooding and frequent
lightning are the greatest weather threats for the next few days.
Winds will pick up a bit and weather will be more seasonal for
next week, with a possible tropical wave for mid-week.
SHORT TERM...Today through Friday...
Hazardous coastal conditions will prevail across the Atlantic
Coastline from the northwest to northeast sections of Puerto Rico,
Culebra, Vieques, and the northern U.S. Virgin Islands. Residents
can expect life-threatening high surfs and isolated coastal
flooding due to the arrival of a long-period northerly swell.
Therefore, High Surf Advisory, Coastal Flood Advisory, and a High
Risk of Rip Currents are in effect for all the north and northeast
facing beaches in Puerto Rico and the U.S. Virgin Islands.
A frontal boundary north of the islands will stall until it
dissipates by the end of the work-week, promoting wet and unstable
weather conditions. A trough aloft will increase instability
furthermore during the afternoon hours today. Under the influence
of this frontal boundary, north of the islands, the steering flow
is forecast to become more south to southeast today. Therefore,
afternoon convection will form along and north of the Cordillera
Central, as well as downwind from the U.S. Virgin Islands. Urban
and small stream flooding is likely today, and cannot rule out
isolated flash flooding. Under the southeasterly wind component,
max temperatures in the low to mid-90s will persist today and
tomorrow, and the heat indices will surpass the 100s degrees
across urban and coastal areas in PR and the USVI each day.
However, winds will become more easterly by Thursday, inducing the
afternoon convection over the western sections. By Friday, winds
should return from the northeast as the boundary weakens in
response to a surface-high-pressure north of us, over the Atlantic
Ocean.
LONG TERM...Saturday through Thursday
The long term forecast for this weekend looks somewhat more
favorable for active weather compared to what models have been
forecasting the past few days. Models have suggested mid to upper
level high pressure building to our west and this is still expected
over the weekend, yet the high pressure center appears to be far
enough west that it may not influence us much. Instead, both the GFS
and ECMWF models suggest weak low pressure over us that could help
enhance convection. Moisture values look fairly average for the
weekend, and definitely sufficient to produce plenty of shower
activity across the region with mildly favorable upper-level
conditions. At low levels, there is expected to be somewhat weak
high pressure over the central Atlantic, so pressure gradients and
associated low-level winds across the region are expected to be
somewhat light and generally easterly. Thus for Saturday, we will
likely see showers and thunderstorms over in the interior and
western Puerto Rico in the afternoon. Winds will turn more out of
the east-southeast for Sunday, so shower activity will then be
expected for northwestern Puerto Rico in the afternoon, as well as
a chance for showers over the San Juan Metro. Urban and small
stream flooding will definitely be a threat given the fairly slow
steering flow.
Heading into the workweek, the winds pick up a bit more at low
levels, which will help showers to move along a bit faster. High
surface pressure really strengthens over the central Atlantic next
week, which is the reason for the increased anticipates. Winds
will stay east southeasterly, so northwestern Puerto Rico and the
San Juan Metro have the best chance for showers. There will still
be plenty of moisture for the atmosphere to work with as well. Not
much change in upper level conditions are expected, so minimally
favorable conditions for thunderstorms remain in the forecast for
next week. Models still suggest a tropical wave moving in for next
Wednesday.
AVIATION...
SHRA/TSRA will continue across the coastal waters due to a frontal
boundary north of the islands. VCSH will affect USVI during the
morning, and some VCSH/VCTS could affect JBQ too. After 23/15z,
SHRA/TSRA will develop across the Cordillera Central and may
impact JSJ/JBQ. Line of SHRA/TSRA will form downwind from the USVI
and may impact IST/ISX btwn 23/15-19z. Winds will continue calm to
light and variable, but an S-SE, but sea breeze will develop after
23/13z.
MARINE...
A northerly swell is affecting the local waters and will continue
through Friday night, causing hazardous seas. Please refer to our
webpage and associated marine products for specific information. Light
to gentle southerly winds will prevail across the regional waters
today, with winds more from the east after today. Showers and
thunderstorms will be possible across the regional waters for the
next few days.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 92 79 92 79 / 50 40 40 40
STT 88 80 88 79 / 30 40 40 50
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late Thursday night for Culebra-
Mayaguez and Vicinity-North Central-Northeast-Northwest-San
Juan and Vicinity-Southeast-Southwest-Vieques.
High Surf Advisory until 6 PM AST Thursday for Culebra-Mayaguez
and Vicinity-North Central-Northeast-Northwest-San Juan and
Vicinity-Southeast.
Coastal Flood Advisory until 6 AM AST Thursday for Mayaguez and
Vicinity-North Central-Northeast-Northwest-San Juan and
Vicinity-Southeast.
High Surf Advisory until 6 AM AST Thursday for Vieques.
VI...High Rip Current Risk through late Thursday night for St Croix-
St.Thomas...St. John...and Adjacent Islands.
High Surf Advisory until 6 PM AST Thursday for St.Thomas...St.
John...and Adjacent Islands.
AM...Small Craft Advisory until 2 PM AST Friday for Atlantic Waters
of Puerto Rico and USVI from 10 NM to 19.5N-Coastal Waters
of Northern Puerto Rico out 10 NM.
Small Craft Advisory until 6 AM AST Friday for Anegada Passage
Southward to 17N-Coastal Waters of Northern USVI and
Culebra out 10 NM-Coastal Waters of Southern USVI Vieques
and Eastern Puerto Rico out 10 NM.
Small Craft Advisory until 8 PM AST Friday for Coastal Waters of
Northwestern Puerto Rico out 10 NM-Coastal Waters of
Southwestern Puerto Rico out 10 NM-Mona Passage Southward
to 17N.
&&
SHORT TERM...JA
LONG TERM....CS
PUBLIC DESK...FRGPerspectivas sobre Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia San Juan PR 514 AM AST miercoles 23 de septiembre de 2020 AMZ710>745-PRZ001>013-240915- San Juan y Vecindad-Noreste-Sureste- Este Interior-Norte Central-Interior Central-Ponce y Vecindad- Noroeste-Oeste Interior-Mayaguez y Vecindad-Suroeste-Culebra-Vieques- Aguas cercanas y mar afuera del Atlantico y Caribe- 514 AM AST miercoles 23 de septiembre de 2020 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Puerto Rico y las aguas costeras del Atlantico. .Dia Uno...Esta tarde y esta noche .Tronadas...Existe la posibilidad de tronadas con lluvia fuerte y vientos en rafagas esta manana sobre el canal de la Mona y las Aguas del Atlantico, y durante la tarde a lo largo y al norte de la Cordillera Central. .Inundaciones...Fuertes lluvias podrian resultar en inundaciones urbanas y riachuelos, y si se forman lluvias bien fuertes no se pueden descartar inundaciones repentinas en las areas urbanas en horas de la tarde. .Oleaje...Una marejada del norte moviendose a traves de los pasajes del Caribe y de las aguas del Atlantico estara aumentando el oleaje de 7 a 12 pies. Olas grandes rompientes entre 10 y 15 pies, pero ocasionalmente mas altas de 15 pies, estaran afectando las playas con orientacion hacia el norte y noreste de Puerto Rico, Culebra y Vieques. .Corrientes Marinas...Existe un riesgo alto de corrientes marinas para las playas con orientaciones al norte y noreste de Puerto Rico, Vieques y Culebra. .Calor...Temperaturas mas altas de lo normal e indices de calor de hasta 107 grados se esperan a traves de las areas urbanas y costeras de Puerto Rico. .Dias dos hasta el siete...jueves a martes Condiciones del tiempo humedas e inestables aumentaran el potencial de aguaceros y tronadas a traves de las islas hasta por lo menos finales de la semana laboral. Inundaciones urbanas y de riachuelos seran posibles cada tarde. Una marejada del norte de largo periodo resultara en condiciones peligrosas a lo largo de las costas del Atlantico por lo menos hasta el viernes. Indices de calor mas alto de lo normal sera posible cada tarde. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion de observadores. Favor de reportar cualquier informacion sobre inundciones. 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-VIZ001-002-240915- San Tomas, San John e Islas Adyacentes-Santa Cruz-Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 514 AM AST miercoles 23 de septiembre de 2020 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Islas Virgenes Estadounidenses y las aguas costeras adyacentes. .Dia Uno...Esta tarde y esta noche .Tronadas...Existe la posibilidad de tronadas con lluvias fuertes y vientos en rafagas esta manana sobre el canal de la Mona, las Aguas del Atlantico y las Islas Virgenes nortenas. .Inundaciones...Lluvias moderadas a fuertes podrian resultar en acumulaciones de lluvia sobre carreteras y en areas de pobre drenaje. .Oleaje...Una marejada del norte moviendose a traves de los pasajes del Caribe y de las aguas del Atlantico estara aumentando el oleaje de 7 a 12 pies. Olas grandes rompientes entre 10 y 15 pies, pero ocasionalmente mas altas de 15 pies, estaran afectando las playas con orientacion hacia el norte y noreste de las islas Virgenes. .Corrientes Marinas...Existe un riesgo alto de corrientes marinas para las playas con orientaciones al norte y noreste de las islas. .Calor...Temperaturas mas altas de lo normal e indices de calor de hasta 107 grados se esperan a traves de las areas urbanas y costeras. .Dias dos hasta el siete...jueves a martes Condiciones del tiempo humedas e inestables aumentaran el potencial de aguaceros y tronadas a traves de las islas hasta por lo menos finales de la semana laboral. Inundaciones urbanas y de riachuelos seran posibles cada tarde. Una marejada del norte de largo periodo resultara en condiciones peligrosas a lo largo de las costas del Atlantico por lo menos hasta el viernes. Indices de calor mas alto de lo normal sera posible cada tarde. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion de observadores. Favor de reportar cualquier informacion sobre inundaciones, vientos, oleaje y corrientes marinas al Servicio Nacional de Meteorologia en San Juan mientras siguen las indicaciones de las autoridades locales y estatales.
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Emergency manager reported Calle Luchetti, Calle Julian Blanco, Avenida Condado, and the Marginal Baldority were flooded.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2020Every state in 2020This day in weather historyWarnings in Puerto Rico, September 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 921880.