An upper-level trough and sufficient moisture combined with local and diurnal effects to generate afternoon shower and thunderstorm, especially across the northwestern quadrant of Puerto Rico and the San Juan metro area. Across the San Juan metro area, a persistent streamer developed and resulted in rainfall accumulations in excess of 3-4 inches.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SJU wrote it up.
An upper-level trough and sufficient moisture combined with local and diurnal effects to generate afternoon shower and thunderstorm, especially across the northwestern quadrant of Puerto Rico and the San Juan metro area. Across the San Juan metro area, a persistent streamer developed and resulted in rainfall accumulations in excess of 3-4 inches.
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 9, 11:54 AM AST, 1 hour 28 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 1154 AM AST Wed Sep 9 2020 .UPDATE...Moderately unstable air with good moisture continues across the area in a slight drying trend. The sounding from the 09/12Z run out of San Juan indicated 1.99 inches of precipitable water. Thunderstorms have been active on and off in the Caribbean but shower activity diminishes when it gets to the coast of Puerto Rico and the Mona Passage. Showers and thunderstorms are still expected to develop across western and interior Puerto Rico and there appears no reason that local urban and small stream flooding will not develop under these showers. Only minor changes to all grids with no changes to general synoptic outlook. && .AVIATION...SHRA/TSRA expected to dvlp aft 09/17Z with TSRA contg thru 09/21Z and SHRA thru 09/23Z ovr land. MVFR conds and mtn obscurations likely with TJMZ/TJBQ effected if only briefly. Sfc winds ESE 8-12 kt with sea breeze influences bcmg aft 09/22Z less than 9 kts with land breezes. Max winds ESE-SE 26-36kt btwn FL330-440 diminish during the period. && .MARINE...No changes to marine discussion. && .PREV DISCUSSION... /issued 706 AM AST Wed Sep 9 2020/ SYNOPSIS... Afternoon showers and isolated thunderstorms will continue through the rest of the week as a upper level trough and an area of low pressure affects the local islands. More opportunities for wet weather are expected next week. Marine conditions remain tranquil with seas up to 5 feet. However, a small northeasterly swell will cause hazardous seas by Friday. SHORT TERM...Today through Friday... An upper level trough and an area of low pressure moving westward just south of the local islands will help to maintain unstable conditions across the region during the rest of today. As a result showers and isolated thunderstorms will affect parts of the coastal waters and portions of the islands during the rest of the morning hours. The aforementioned feature along with the available moisture brought in by the prevailing southeasterly wind flow will favor afternoon convection over parts of the interior and northwestern quadrant of Puerto Rico. Parts of the San Juan metro area may also experience brief periods of afternoon showers but lesser activity is expected. Urban and small stream flooding will be possible with the heavy rains in areas of persistent rainfall. By late Thursday, an upper level ridge will sink southwards across the region from northwest resulting in more stable conditions aloft. Meanwhile at the surface, the Atlantic high pressure ridge will migrate farther westward into the west and southwest Atlantic, Tropical Storm Paulette is forecast to lift northwestwards across the tropical Atlantic and well north of the region late Thursday through the end of the work week. This overall and expected scenario should induce a light to moderate east to northeast wind flow beginning late tonight and continuing through Friday. Consequently, expect an overall drier weather pattern with decreasing layered precipitable water values and a gradual erosion of low level moisture across the region for Thursday and Friday. Occasional patches of passing low clouds and early morning showers steered by the prevailing northeast winds is however forecast to persist although a drier air mass is so far expected during the rest of the period. Locally and diurnally induced isolated to scattered afternoon shower activity should to be focused over the central interior and southwest quadrant of Puerto Rico each day with lesser shower activity expected elsewhere, as mostly sunny and fair weather skies will prevail based on latest model guidance. LONG TERM...Saturday through Wednesday... An upper low will hold over the region through Sunday. This will cause enough instability aloft to promote showers and isolated thunderstorms over the islands during the weekend. Models are unclear on which day over the weekend will be more active, but the usual afternoon thunderstorm activity over western Puerto Rico can be expected. For Saturday, it appears thunderstorms will focus over southwest Puerto Rico. Then winds shift for Sunday, causing the activity to focus over northwest PR. Thereafter, active weather should continue as models suggest moisture will get pulled up from the south for Monday and Tuesday. Upper level atmospheric conditions appear mildly favorable for thunderstorm activity, so again localized flooding and lightning will be the main threats to start the workweek. Uncertainty is very high for the forecast heading into the middle of the workweek. NHC is currently monitoring two tropical systems over and near the central tropical Atlantic. These systems are expected to remain far from the local area. NHC is also monitoring a wave over western Africa with a high potential for cyclonic development in the next five days. As of now, latest model guidance shows high uncertainty regarding posible intensification and track of this system. However, as we are already into the peak of the Hurricane season, it is highly recommended to continue monitoring the latest official information issued by NHC. AVIATION... VFR at all terminals but with SCT ocnl BKn lyrs nr FL022...FL050 ..FL080 and SHRA/Isold TSRA ovr the regional waters and btw E PR and the U.S.VI. Few SHRA will move inland ovr coastal areas of islands with VCSH at TISX/TIST/TJSJ TIL 09/14z. Brief Mtn Top obscr psbl ovr Ern PR w/SHRA and SCT low cld lyrs. Aftn convection ovr the interior and NW quadrant of PR fm 09/16Z-09/23z with VCSH/VCTS psbl at TJMZ/TJBQ and slight chance of isold VCTS at TJSJ. Sfc wnd will be calm to LGT/VRB bcmg fm SE 10-15 kts but with some sea breeze variations aft 09/14z. MARINE... Tranquil marine conditions are expected to prevail for the next couple days, with seas up to 5 feet and winds up 15 knots from east-southeast. A northerly swell will increase seas across the islands tomorrow and may become higher by Friday or Friday night. For the beachgoers, there is a low risk of rip currents for the beaches across the local islands. && .PRELIMINARY POINT TEMPS/POPS... SJU 79 89 78 89 / 40 30 40 40 STT 81 90 80 90 / 30 30 30 30 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && SHORT TERM...WS LONG TERM....MB PUBLIC DESK...LIS
Perspectivas sobre Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia San Juan PR 435 AM miercoles 9 de septiembre de 2020 AMZ710>745-PRZ001>013-100845- 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- 435 AM miercoles 9 de septiembre de 2020 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Puerto Rico y las aguas costeras del Atlantico. .Dia Uno...Hoy y esta noche .Tronadas... Existe una probabilidad de tronadas con fuertes lluvias y vientos en rafaga a traves de sectores del interior y norte de Puerto Rico durante la tarde, al igual que alrededor del area metro de San Juan y Vieques. .Inundaciones...Lluvias fuertes podrian generar inundaciones urbanas y de pequenos riachuelos, y tambien acumulaciones de lluvia sobre carrateras y en areas de pobre drenaje. Oleaje...Una marejada del norte aumentara el oleaje hasta 5 pies, ocasionalmente hasta 6 pies, principalmente sobre las aguas mar afuera del Atlantico noreste. .Calor...Vientos del sureste y condiciones humedas resultaran en indices de calor por encima de lo normal de entre 102 y 107 grados en algunas areas. .Dias dos hasta el siete...miercoles a lunes Hasta por lo menos el jueves, los efectos locales y diurnos contribuiran al desarrollo de tronadas aisladas sobre el oeste de Puerto Rico. Como resultado, inundaciones menores urbanas y de riachuelos o acumulacion de agua en carreteras y en areas de drenaje pobre seran posibles. Se pronostica un riesgo de moderados a alto de corrientes marinas para algunas playas desde el jueves en adelante. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion de observadores. Favor de reportar cualquier informacion sobre inundaciones y corrientes marinas al Servicio Nacional de Meteorologia en San Juan mientras siguen las indicaciones de las autoridades locales y estatales. AMZ715-725-VIZ001-002-100845- San Tomas, San John e Islas Adyacentes-Santa Cruz-Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 435 AM miercoles 9 de septiembre de 2020 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Islas Virgenes Estadounidenses y las aguas costeras adyacentes. .Dia Uno...Hoy y esta noche Oleaje...Una marejada del norte aumentara el oleaje hasta 5 pies, ocasionalmente hasta 6 pies, principalmente sobre las aguas mar afuera del Atlantico noreste. .Calor...Se esperan indices de calor sobre lo normal entre 102 y 107 grados en algunas areas. .Dias dos hasta el siete...miercoles a lunes Se pronostica riesgo moderado de corrientes marinas para algunas playas desde el jueves en adelante. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion de observadores. Favor de reportar cualquier informacion sobre corrientes marinas al Servicio Nacional de Meteorologia en San Juan mientras siguen las indicaciones de las autoridades locales y estatales.
The San Juan radar (TJUA), 34 km away, was scanning. The volume nearest the first event began at 17:19 UTC.
12 flash flood, 1 flood. Local standard time, as filed.
Flooding reported along Road PR-165 after the Expreso de Diego Bridge near the Metropolitan Detention Center.
Flooding reported along Avenida Pi ero intersection with Calle Andalucia in the traffic light in front Baskin Robbins. Several cars were partially surmerged in flood waters.
Flooding reported along Roads 28 and 5 in the Urbanization of Villa Nevares behind Cosvi.
Flooding reported along Avenida de Diego intersection with Avenida Franklin Delano Roosevelt.
Flooding reported in Avenida Escorial. Aqua Body shop was flooded with 5 people trapped inside the facility.
Flooding reported in Calle 10 intersection with Calle 33.
The central building in the Centro Medico de Puerto Rico complex had the basement flooded.
Residence flooded along Calle Colon. Three people were trapped inside.
Calle 27 right beside a baseball park, car submerged trapping people inside.
Flooding reported along Calle Manila.
Flooding reported along Avenida Escorial by the Refricentro entrance. One person trapped.
Flooding reported in a residence along Calle Jose Qui ones in Rio Piedras. 1 person with pet trapped inside residence.
Expreso Las Americas from San Juan to Caguas, near Centro Medico, was flooded. Vehicle submerged with one person trapped inside.
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: 920632, 920634, 920633, 920637, 920638, 920639, 920641, 920642, 920636, 920640, 920643, 920644, 920635.