A tropical wave moved across the area. The associated moisture along with strong daytime heating and local effects generated enhanced shower and thunderstorm activity, mainly across the north-central municipalities of Puerto Rico.
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The episode as NWS SJU wrote it up.
A tropical wave moved across the area. The associated moisture along with strong daytime heating and local effects generated enhanced shower and thunderstorm activity, mainly across the north-central municipalities 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 Sep 3, 4:36 PM AST, 1 hour 4 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 436 PM AST Fri Sep 3 2021 .SYNOPSIS...As a tropical wave moves away, a drier air mass is expected to encompass the local islands, bringing dry and stable weather conditions much of the weekend into early the next work week. Hurricane Larry is expected to pass by the region well to the northeast during the first half of next week. Hazardous marine conditions are expected as swells generated by this system reach the regional waters. & .SHORT TERM...Tonight thru Sunday... A mid to upper level ridge will continue to weaken under pressure from a meandering TUTT low to the north. This feature will continue to meander north of the area through much of the forecast cycle. At low levels...a weak tropical wave and associated moisture will continue to prevail across the local islands. However, as this wave moves away overnight, a drier air mass will encompass the forecast area by midday Saturday. Based on the latest guidance, the precipitable water values are expected to drop between 1.40 and 1.5 inches by Saturday afternoon. As a result, under this evolving pattern, continue to expect passing showers across portions of eastern Puerto Rico and the US Virgin islands as well as the local waters through Saturday morning. Although, a drier air mass is then expected Saturday and Sunday, locally induced afternoon showers and isolated thunderstorms are still expected each day. .LONG TERM.../issued 510 AM AST Fri Sep 3 2021/ Mon thru Fri... Much of the long-term period is dominated by the (indirect) impacts of Hurricane Larry. The system is expected to pass by the region well to the northeast during the first half of next week. Patches of moisture will make their way into the region from time to time during the first part of the week. Precipitable water values are forecast to remain near normal during this time, or possibly just below normal. Meanwhile, ridging aloft will limit instability; on the whole, a typical shower pattern is expected, but activity is likely to be somewhat inhibited. Increasing moisture is expected late Wednesday, as moisture is dragged up from the ITCZ towards Larry, which is likely to be to our northeast/north-northeast at that point. However, model guidance has backed off on how much moisture makes it over the region, and slowed down the arrival compared to yesterday's model runs. Even so, some moisture is likely during the second half of the week; uncertainty is substantial with respect to how much and for when. In addition to the moisture increase, conditions aloft are anticipated to become less stable during this time, under the influence of troughing associated with the tropical cyclone. This will aid in the development of convection, as well as in the generation of a deeper moist layer over the area. As such, increased shower activity is expected. There is above-normal uncertainty with respect to the forecast, as alluded to previously. This is largely due to the general dependency of conditions here on the track and intensity of Larry, as well as conditions from the periphery of the system, and how much moisture the system is able to drag up with it. Confidence with respect to the location of peak activity is also below normal, due to the effects of Larry on the winds over the region, largely associated with the system's impacts on the location of the surface ridge to the north. As such, the details with this forecast are likely to change going forward. Behind this increased moisture is a drier air mass with patchy moisture. Currently this looks likely to affect the region Thursday into Friday, with decreased shower activity. On Friday, a tropical wave is forecast to bring moisture to the region. Meanwhile, conditions aloft will be more conducive to convective development. An increase in shower activity is expected, lasting into the weekend. && .AVIATION...VFR conditions will prevail the rest of the forecast period. However, SHRA/TSRA will develop across the interior, north, and west of the Cordillera later this afternoon into the evening. JBQ has a TEMPO between 03/19-21z due to possible MVFR conditions. E to ESE winds between 15 and 18 knots with sea breeze variations will persist thru 03/23z, becoming calm to light and vrb afterward. Winds will return from the E at 10 to 15 knots tomorrow (04/13z). && .MARINE...Choppy marine conditions will persist across the local waters through the weekend, with seas up to 5 feet and winds up to 20 knots expected. Hazardous marine conditions are expected by early next week as swells generated by Hurricane Larry reach the regional waters. && .PRELIMINARY POINT TEMPS/POPS... SJU 80 91 80 90 / 50 40 20 20 STT 81 89 80 91 / 30 20 20 30 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && AVIATION...CAM SHORT TERM....OMS
Perspectivas sobre las Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia en San Juan PR 517 AM AST viernes 3 de septiembre de 2021 AMZ710>745-PRZ001>013-040930- 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- 517 AM AST viernes 3 de septiembre de 2021 Esta Perspectiva sobre las Condiciones Peligrosas del Tiempo es para Puerto Rico y las aguas costeras adyacentes del Atlantico. .Dia Uno...Hoy y esta noche .Tronadas...Existe el potencial de tronadas con lluvia fuerte y rafagas de vientos breves esta tarde a traves de sectores del interior, noreste y oeste de Puerto Rico. .Inundaciones...Lluvia de moderada a localmente fuerte pudiera resultar en inundaciones urbanas y de riachuelos. .Corrientes marinas...Existe riesgo moderado de corrientes marinas para la costa norte de Puerto Rico y las costas norte y este de Culebra. .Calor...Se esperan indices de calor por encima de lo normal entre 102 y 107 grados a traves delas regiones urbanas y costeras. .Dias dos hasta el siete...sabado a jueves Se espera que indices de calor por encima de lo normal continuen durante los proximos dias. El riesgo moderado de corrientes marinas se extendera y continuara durante el fin de semana hasta temprano la semana proxima. Las condiciones maritimas y costeras posiblemente se deterioraran temprano la semana proxima. .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-VIZ001-002-040930- San Tomas, San John e Islas Adyacentes-Santa Cruz-Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 517 AM AST viernes 3 de septiembre 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 inundaciones urbanas y de riachuelos. .Corrientes marinas...Existe riesgo moderado de corrientes marinas para Cramer Park. .Calor...Se esperan indices de calor por encima de lo normal entre 102 y 107 grados a traves de areas urbanas y costeras. .Dias dos hasta el siete...sabado a jueves Se espera que indices de calor por encima de lo normal continuen durante los proximos dias. El riesgo moderado de corrientes marinas se extendera y continuara durante el fin de semana hasta temprano la semana proxima. Las condiciones maritimas y costeras posiblemente se deterioraran temprano la semana proxima. .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), 81 km away, was scanning. The volume nearest the first event began at 21:37 UTC.
2 flood, 1 flash flood. Local standard time, as filed.
Two lanes of Road PR-2 near Corporacion del Fondo del Seguro del Estado were flooded.
Emergency managers reported Rio Santiago out of its banks. People from 3 houses were evacuated at Parcelas Luis Rodriguez Olmo as a result.
Emergency managers reported Road PR-129 impassable near CESCO Arecibo.
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, September 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: 976060, 976064, 976067.