A tropical wave moved across the area, increasing convergence at the lower levels. Later in the period, low level moisture was provided by the proximity of a surface trough.
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The episode as NWS SJU wrote it up.
A tropical wave moved across the area, increasing convergence at the lower levels. Later in the period, low level moisture was provided by the proximity of a surface trough. Additionally, an upper level low approached from the northeast, providing instability aloft, as high pressure at all level weakened.
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 Aug 21, 4:42 AM AST, 3 hours 18 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 442 AM AST Sun Aug 21 2022 .SYNOPSIS... A tropical wave passing south of the islands and trade wind convergence is resulting in numerous showers and scattered thunderstorms across region. Another active day of weather is expected today with an elevated threat for urban and small stream flooding, with localized flash flooding and mudslides in areas of steep terrain. Tomorrow more unstable weather is forecast as an upper level low moves close to the region and then a seasonal wet weather pattern of passing showers and afternoon storms is expected for the majority of the week. A strong tropical wave may pass over the islands at the end of the long term period. && .SHORT TERM...Today through Tuesday... A tropical wave moving across the central Caribbean and trade wind convergence across the eastern Caribbean are producing numerous showers and scattered thunderstorms across region. The heaviest activity has remained across the Caribbean waters, but showers with periods of moderate to locally heavy rainfall moved at times across portions of southeastern PR, and across the USVI. Since midnight, the doppler radar estimated near an inch of rain across portions of eastern PR. Latest Blended-Percent of Normal Total Precipitable Water (TPW) indicated a broad area of 110%-130% of above TPW between the local area and just east of the Leeward Islands. Therefore, higher moisture content will continue to advect across the islands today, and another active weather day is expected with scattered to locally numerous showers and isolated thunderstorms affecting portions of the islands at times. There is an elevated threat for urban and small stream flooding, with localized flash flooding and mudslides in areas of steep terrain. Unstable conditions will continue through early in the week, as an upper-level low moves close to the region from the central Atlantic. An induced surface trough will move across the northeastern Caribbean by Monday, and weakening of the surface high across the western Atlantic will promote a light to moderate and moist southeasterly wind flow across local area. Therefore, an overall wet pattern will continue across the islands through at least Tuesday. && .LONG TERM...Wednesday to Monday... The ridge phase of the African Easterly Jet arrives on Wednesday and it brings patchy moisture over region. No prominent feature is present in the mid to upper levels besides a TUTT-low to the north that may excite more showers over the Atlantic Waters but nothing significant. Wind flow will prevail from the East-southeast around 10-15 knots with seabreeze variation as a high pressure system dominates the Northern Atlantic Basin. The typical weather pattern of passing showers and afternoon convection over interior/western Puerto Rico is expected through Friday. Local effects and diurnal heating may amplify the available moisture so there could be some standout periods of rainfall during this time. Saturday afternoon a snap of moisture is expected to reach the islands and provide a wetter evening compared to the days before. Winds continue from the east at moderate speeds and atmospheric stability seems normal so an increase of passing showers and stronger afternoon thunderstorms will be the result of this increase in moisture. Currently the NHC is monitoring an area of development that GFS model guidance is suggesting will begin affecting the region by Sunday afternoon. It appears as a robust tropical wave that has the potential to bring heavy rainfall and strong winds for the beginning of next week. GFS model guidance has the axis passing by Monday night into Tuesday morning, a day later in timing than yesterday. This forecast will change due to the fickle nature of weather forecasting models this far out, yet a strong tropical wave is expected sometime during the end of the long term period. The results of this is a veering of the winds and a very saturated, unstable atmosphere up to the tropopause. && .AVIATION...VFR conds expected but SCT SHRA and iso TSRA may continue to affect the USVI and TJSJ/TJNR terminals during the morning hours. Mtn top obscd over eastern PR and SCT-BKN lyrs nr FL025...FL050 ovr regional waters and enroute btw islands are expected. Brief periods of MVFR are possible due to low CIGS and reduced VIS. Winds expected to increase btw 12-16 kt from the east with higher gusts and sea breeze variations aft 14Z. && .MARINE... A high pressure system stretched across the Central Atlantic continues to promote moderate to locally fresh easterly winds across the region. These winds are producing a local wind swell that is resulting in choppy seas up to around 5 feet. Winds are expected to decrease in strength and become more southeasterly tomorrow. Passing showers and isolated thunderstorms continue to effect the local waters with most of the concentration in the Caribbean waters today. A very small northerly swell is expected to arrive overnight on Monday. Across Puerto Rico and the US Virgin Islands, a moderate risk of rip currents exist along most northern and eastern facing coastlines and the risk is low elsewhere. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. && SHORT TERM...DS LONG TERM....RC
Perspectivas sobre las Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia en San Juan PR 507 AM AST domingo 21 de agosto de 2022 AMZ710>745-PRZ001>013-220915- 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 del Caribe- 507 AM AST domingo 21 de agosto de 2022 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Puerto Rico y las aguas costeras adyacentes. .Dia Uno...Hoy y esta noche .Tronadas...Tronadas de aisladas a dispersas son posibles a traves de sectores del este, central y oeste de Puerto Rico. Este atento a las tronadas en su area y preparese para refugiarse. .Lluvia Excesiva...Inundaciones de areas urbanas, carreteras y riachuelos. Inundaciones repentinas aisladas son posibles. .Calor Excesivo...Se esperan indices de calor entre 102 a 108 grados a traves de las areas costeras del norte y oeste de Puerto Rico. El agotamiento por calor es posible con una exposicion prolongada. .Corrientes Marinas...Las corrientes marinas amenazantes a la vida son posibles a lo largo de las zonas de olas rompientes de las playas del norte y este de Puerto Rico. .Dias dos hasta el siete...lunes a sabado Se espera un riesgo moderado de corrientes marinas para la segunda mitad de la semanan laboral a traves de las playas del norte y este de la isla. El riesgo puede aumentar a alto tarde en la semana debido a una marejada pequena del norte. Una vaguada inducida aumentara la actividad de aguaceros y tronadas a traves de las islas el lunes. De lo contrario, se esperan tronadas a traves del oeste de Puerto Rico cada tarde. Un riesgo leve de calor, debido a indices de calor en los bajos 100 grados a traves de la costa norte y oeste de Puerto Rico, es posible cada dia entre tarde en la manana y temprano en la tarde. .Comunicado sobre informacion reportada por observadores... Los observadores deben reportar cualquier lluvia fuerte o inundaciones al Servicio Nacional de Meteorologia en San Juan. AMZ715-725-VIZ001-002-220915- San Tomas, San John e Islas Adyacentes-Santa Cruz- Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 507 AM AST domingo 21 de agosto de 2022 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Islas Virgenes Estadounidenses y las aguas costeras adyacentes. .Dia Uno...Hoy y esta noche ..Tronadas...Tronadas de aisladas a dispersas son posibles a traves de las aguas cercanas de las islas, algunas de estas tronadas podrian moverse sobre las islas. Este atento a las tronadas en su area y preparese para refugiarse. .Lluvia Excesiva...Acumulacion de agua en carreteras y en areas de pobre drenaje son posibles a traves de las islas. .Calor Excesivo...Indices de calor de hasta 105 grados son posibles a traves del sur de St. Croix. Agotamiento por calor es posible con una exposicion prolongada. .Corrientes Marinas...Las corrientes marinas amenazantes a la vida son posibles a lo largo de las zonas de olas rompientes de las playas del este de St. Croix. .Dias dos hasta el siete...lunes a sabado Se espera que el riesgo de corrientes marinas aumente para tarde en la semana laboral debido a la llegada de una marejada del norte. Una vaguada inducida aumentara la actividad de aguaceros y posibles tronadas aisladas a traves de las islas el lunes y el martes. .Comunicado sobre informacion reportada por observadores... Los observadores deben reportar cualquier lluvia fuerte, inundaciones o deslizamientos de tierra al Servicio Nacional de Meteorologia en San Juan.
The San Juan radar (TJUA), 27 km away, was scanning. The volume nearest the first event began at 11:58 UTC.
19 flood, 5 debris flow, 3 flash flood. Local standard time, as filed.
A trained spotter called to report one lane of Road-3 near Home Depot flooded.
Emergency Managers reported a residency being affected by flooding in Barrio Las Cuevas, near Road PR-181.
Emergency Managers reported that Ave. De Diego was flooded near Suiza Dairy.
Emergency Managers reported That Road PR-19 was flooded, near San Patricio Plaza.
Emergency Managers reported a small stream out of its banks in Ramos Jordan, Puerto Nuevo.
Emergency managers reported several road flooded at urb. Villa Nevares.
Emergency Managers reported a landslide at Road PR-423, Barrio Sonador in Alto Sano.
Emergency Managers reported a landslide in Road PR-123 Bo. Sonador, Alto Sano.
Emergency Managers reported a mudlside in PR-109 in Barrio Sonador.
An NWS Employee reported that one lane of PR-52 near Montehiedra, was impassable due to flooding.
Emergency Managers reported Road PR-175 Km 9.3 flooded.
Emergency Managers reported a landslide at Barrio Alto Sano, Sector Los Guineos, close to Road PR-109.
Emergency Managers reported a landslide at PR-435, Barrio Calabaza, Sector Sancho Grande.
Emergency Managers reported a Landslide near Road PR-181, km 8.87, Barrio Dos Bocas. The landslide undermined an electrical post, leaving several communities without power.
A broadcast member posted on social media a report of a landslide in PR-149, Barrio Jaguas.
An NWS employee reported that Road PR-887, near PR-3 and a Walgreens was partially flooded, with one lane almost impassable.
Emergency Managers reported that Quebrada Margarita was out of its banks, flooding areas near Ramon Jordan in Puerto Nuevo.
A report received by a vipermail indicated flooding around Ave. de Diego, close to Hospital San Francisco.
Emergency Managers reported flooding near Road PR-19, near a Total Gas Station.
Emergency Managers reported Quebrada San Francisco, close to Hospital San Francisco was out of its banks at Ave. de Diego.
Emergency Managers reported flooding along PR-1, and Highway 52. People were trapped in a car.
Emergency Managers reported Ave. Simon Madera, Intersecting Calle Alegria was flooded.
Emergency Managers reported Calle Juncos in Villa Palmera flooded.
Emergency Managers reported flooding at Ave. Monte Carlo, near Colegio Calasanz.
Emergency Managers reported flooding at a road near Pep Boys and 65 de Infanteria, close to Urb. Las virtudes.
A member from media shared in social media a video of all lanes in Road 65 de Infanteria, intersection with PR-181 flooded, and these roads were impassable.
A media reported shared a post on social media indicating that Quebrada Grande was overflowing at PR-404 in Barrio Cruz, Moca.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2022Every state in 2022This day in weather historyWarnings in Puerto Rico, August 2022
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: 1045251, 1045253, 1045219, 1045220, 1045229, 1045230, 1045235, 1045236, 1045243, 1045231, 1045245, 1045249, 1045250, 1045247, 1045256, 1045265, 1045269, 1045473, 1045475, 1045478, 1045480, 1045482, 1045484, 1045490, 1045491, 1045494, 1045495.