A Tropical Upper Tropospheric Trough near the area and near normal moisture values combined with strong daytime heating and local effects to generate shower and thunderstorm activity across the San Juan metro as well as western and northwestern portions of Puerto Rico.
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The episode as NWS SJU wrote it up.
A Tropical Upper Tropospheric Trough near the area and near normal moisture values combined with strong daytime heating and local effects to generate shower and thunderstorm activity across the San Juan metro as well as western and northwestern portions of Puerto Rico.
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 2, 10:43 AM AST, 2 hours 7 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 1043 AM AST Mon Aug 2 2021 .UPDATE... Partly cloudy skies were observed over the islands this morning and will continue through the day. TJUA radar shows showers scurrying across the Atlantic and Caribbean waters. The shower activity will move inland later this afternoon. A TUTT low is providing upper-level instability over the region; the instability and low- level moisture convergence over the island will promote organized convection over portions of western and interior areas of Puerto Rico today. The GFS and ECMWF show 500 mb heights ranging from -6 to -7.5 degrees Celsius, with above-normal precipitable water over Puerto Rico. The combination above will aid in the development of showers and isolated thunderstorms. Numerous showers and isolated thunderstorms are expected over the western areas of the island; elsewhere, scattered to isolated showers and isolated thunderstorms over the eastern and north- central parts of Puerto Rico. Deterministic and probabilistic guidance has 1 to 2 inches of rainfall for the western and interior areas of Puerto Rico and up to 3 inches in isolated areas. Therefore, moderate to heavy rain and urban and small stream flooding is likely. East to southeast winds will cause daytime high temperatures to reach the upper 80s to lower 90s in lower elevations, and the upper 70 to lower 80s in higher elevations. Conditions should improve by sunset as surface heating begins to wane. && .AVIATION... VFR early in the forecast period. SHRA/TSRA expected to develop in and around the PR terminals from 16z-22z, this could lead to tempo MVFR conditions and mtn top obscd across the island. Periods of RA/VCSH expected across the USVI terminals and SCT cigs btw FL025-FL050. Low level winds from the east at 8-15 kt with sea breeze variations will continue through this afternoon. && .MARINE... Mariners can expect relatively tranquil marine conditions through much of the week, with seas below 4 feet and winds at less than 15 knots. However, thunderstorms will develop each afternoon, especially near the Mona Passage and the Atlantic Coastal waters. && .PREV DISCUSSION... /issued 506 AM AST Mon Aug 2 2021/ SYNOPSIS...Surface high pressure across the north central Atlantic will continue to yield a gentle to moderate easterly wind flow during the next several days. A TUTT low will drift westward from the Atlantic Ocean into the Northeast Caribbean through Tuesday. Increasing moisture will help in the development of showers and isolated thunderstorms across the local forecast area. SHORT TERM...Today through Wednesday... A more typical seasonal weather pattern is expected to prevail for today. The drier air at the mid levels is expected to erode due to deeper moisture over the islands. At surface, a high pressure near the Azores will promote east-northeast trades. Thus, showers will continue to advect during the early morning hours. Then, a shift in winds, more to the east-southeast and the available moisture will combine with diurnal heating and local effects to generate scattered to numerous showers over the northwestern quadrant of Puerto Rico. A TUTT-low will move westward from the Atlantic Ocean into the Northeast Caribbean today through Wednesday. Model guidance suggest and increase in moisture (PWAT values around 1.7 inches)for Tuesday and Wednesday. There is good potential for isolated thunderstorm activity during the afternoons mainly due to daytime heating, local forcing and the proximity of the TUTT. Rainfall accumulations could be enough to cause minor urban flooding with the heaviest rains. This will increase the potential for urban and small stream flooding. LONG TERM...Thursday through Tuesday... On Thursday the GFS model is suggesting a drop on precipitable water across the region but a wind surge will help increase the moisture across the local area between late Thursday night and Friday. This weather feature will help increase the showers coverage across the region through the weekend. A tropical wave is forecast to move across the Caribbean waters between Monday and Tuesday. Although the bulk of moisture associated to the wave will remain south of the local islands some moisture increase is expected. AVIATION...Mainly VFR conditions will prevail across all terminals during the next 24 hours. However, the SHRA in route will cause VCSH across most of the local terminals and TEMPO reductions in VIS are possible during the afternoon for TJBQ due to VCTS and SHRA. The winds will be light and variable overnight, but then gradually turning ESE during the day. MARINE...Mariners can expect tranquil marine conditions through much of the week, with seas below 4 feet and winds at less than 15 knots. However, thunderstorms will develop each afternoon, especially near the Mona Passage and the Atlantic Coastal waters. FIRE WEATHER...Although an increase in the available moisture is expected, relative humidity values may still fall into the lower to mid 50s between the late morning and early afternoon hours. Lack of wetting rains in the forecast across these areas will also support further drying of soils and fuels. As a result, KBDI and 10-hour fuel moisture values should remain within fire danger conditions. Taking these factors into consideration, including the local wind flow peaking at 15-20 mph and considering the chance for lightning activity in the area, elevated fire weather conditions are expected across the southern coastal plains of Puerto Rico today. For this reason, a Fire Danger Statement has been issued. && .PRELIMINARY POINT TEMPS/POPS... SJU 88 77 89 78 / 40 50 30 40 STT 90 78 88 78 / 40 40 30 30 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && SHORT TERM...DS LONG TERM....TW PUBLIC DESK...OM
Perspectivas sobre Condiciones Peligrosas del Tiempo...Correccion Servicio Nacional de Meteorologia en San Juan PR 502 AM AST lunes 2 de agosto de 2021 AMZ710>745-PRZ001>013-030845- 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- 502 AM AST lunes 2 de agosto 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 .Tronadas...Existe el potencial de tronadas aisladas con lluvias moderadas a localmente fuertes esta tarde a traves de sectores del noroeste de Puerto Rico. .Inundaciones...Lluvias fuertes podrian resultar en inundaciones urbanas y de riachuelos a traves de sectores del noroeste de Puerto Rico. .Corrientes Marinas...Existe un riesgo moderado de corrientes marinas para las playas del norte central de Puerto Rico. .Incendios Forestales...Se espera un aumento en el peligro de incendios forestales a traves de las planicies costeras del sur de Puerto Rico. .Calor...Temperaturas y humedad por encima de lo normal resultaran en indices de calor entre 102 y 105 grados, mayormente a traves de areas costeras de los municipios del norte central de Puerto Rico. .Dias dos hasta el siete...martes a domingo Se espera el potencial de actividad de tronadas aisladas hasta el martes. Indices de calor entre 102 y 105 grados son posibles durante los proximos dias. Se espera un peligro elevado de incendios forestales a traves de las planicies costeras del sur de Puerto Rico durante los proximos dias. .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-VIZ001-002-030845- San Tomas, San John e Islas Adyacentes-Santa Cruz-Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 502 AM AST lunes 2 de agosto 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 .Inundaciones...Lluvias fuertes pudieran resultar en acumulacion de agua en carreteras y areas bajas. .Dias dos hasta el siete...martes a domingo Existe un riesgo moderado de corrientes marinas para el extremo este de Santa Cruz para finales de la semana laboral. .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.
The San Juan radar (TJUA), 31 km away, was scanning. The volume nearest the first event began at 16:49 UTC.
1 flash flood, 1 heavy rain. Local standard time, as filed.
Three vehicles were stranded under flood waters along Calle 31, with people trapped inside the vehicles.
A family of 6 people from Orlando were rescued from a water surge at the Gozalandia Waterfall.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2021Every state in 2021This day in weather historyWarnings in Puerto Rico, August 2021
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: 975935, 975936.