A weak trough near the Leeward islands was maintaining a weak steering flow over the local islands. Instability aloft was increasing as mid level temperatures cool down.
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The episode as NWS SJU wrote it up.
A weak trough near the Leeward islands was maintaining a weak steering flow over the local islands. Instability aloft was increasing as mid level temperatures cool down. The combination of these factors, along with strong diurnal heating and enough moisture in the lower levels resulted in very strong showers and isolated thunderstorms over the area. Several reports of mudslides and flooding were received.
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 Apr 27, 8:58 PM AST, 7 hours 2 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 858 PM AST Thu Apr 27 2023 .UPDATE... Shower activity gradually decreased along southern Puerto Rico, but some lingered over the eastern municipalities. These showers left accumulations of 1-1.5" throughout the period. Conditions will continue to improve tonight and skies will clear out. A similar pattern will persist tomorrow, with quiet conditions in the morning and activity developing in the afternoon. It will be hot too, with temperatures in the 90s and heat indices above 102 degrees, especially for the urban and coastal areas of northern Puerto Rico. && .AVIATION... Mainly VFR conditions are expected to prevail. Light winds below 5 knots are expected to persist through 12-14Z, then winds will pick up, out of the E at 10 knots or less. SHRA expected to develop along the Cordillera Central after 18Z, causing mountain obscuration and VCSH for TJSJ/TJPS until 22Z. && .MARINE... Tranquil marine conditions will persist for the next few days, although a small northerly swell continues to invade the local waters. Recent observations show seas 3 to 4 feet, and these values will persist along the nearshore buoys. && /PREV DISCUSSION/ .SYNOPSIS...Rains from afternoon showers with isolated thunderstorms development could lead to flooding of urban areas and small streams to possible localized flash floods and mudslides. More stable weather conditions are anticipated for the weekend, but afternoon shower development remains likely. Heat indices of 102-107 degrees are likely each afternoon, primarily across northern and western sections. Increasing winds and a small northerly swell will yield life-threatening rip currents early next week. && .SHORT TERM...Today through Saturday... Afternoon moderate to locally heavy rains could lead to excessive rain hazard risk at limited to elevated levels each afternoon, mainly across the interior to northern sections of Puerto Rico. Limited excessive heat hazard risk levels are likely each afternoon. Although drier air entrainment holds at mid-levels, a weak trough will maintain marginally unstable weather conditions while yielding to a westerly mid-level flow. Light and predominantly southerly surface steering flow at 5-15 mph will persist tonight, becoming more east-southeasterly on Friday and Saturday. Under this flow, a plume of low-level moisture will reach the local islands, causing precipitable water values to remain normal to slightly above-normal seasonal levels. Remnants from the afternoon convection will remain over land areas through near sunset, particularly over the east. After that, and without a solid atmospheric forcing, fair weather conditions under clear to partly cloudy skies and limited shower activity should prevail during the overnight and morning hours. By late Friday morning into the afternoon, sufficient moisture levels, local effects, and daytime heating will fuel showers with possible isolated thunderstorm development. Following the general steering flow, the focus of this activity and rainfall distribution should favor central Puerto Rico, with some showers steered over northern and eastern sections, including the San Juan metropolitan area, by the mid- level flow. Moderate to locally heavy rains, generating isolated rainfall totals exceeding an inch or two, could lead to limited to elevated excessive rainfall hazard risks. Localized flash floods and mudslides are possible. A similar weather pattern with similar showers and rainfall distribution will persist, stretching more eastward on Friday and northward on Saturday, as suggested by the expected mid-level steering flow. However, a strengthening mid-level ridge pattern may gradually lead to hostile conditions for deep convective development as it meanders northeastward into the north-central Caribbean region during the weekend. Daily temperature variations will range from the upper 80s to around 90 degrees across coastal and other urban areas in the daytime to the upper 50s to about 60 degrees across higher elevations. A southern to a southeastern component in the general flow in a high moisture content environment could yield heat indices around 102-107 degrees, particularly across northern and western sections of Puerto Rico in the afternoon. && .LONG TERM...Sunday through Friday... From previous discussion issued at 531 AM AST Thu Apr 27 2023 For the most part, a seasonal weather pattern can be anticipated for most of the long-term period, with moisture content fluctuating from below-normal to near-normal levels. Tuesday will be the driest of the forecast period, with precipitable water values decreasing to as low as 1.10 inches and 700-500 mb relative humidity plummeting to below 15%. Dynamically stable conditions will persist as a surface high pressure and a mid to upper-level ridge build across the local area by Sunday through midweek. So far, the forecast calls for mainly fair weather conditions with limited shower activity across the local islands. However, locally induced afternoon showers will remain possible through at least Wednesday but should be focused mainly on portions of interior and western/northwestern Puerto Rico. Much warmer temperatures can be expected by Monday, persisting through the rest of next week, as winds become more southeasterly. By Late Wednesday and through at least Friday, model guidance suggests a shift in the weather pattern due to a building mid- to upper-level trough just north of the region and increased moisture convergence as the associated frontal boundary approaches from the northwest. The prevailing winds will continue southeasterly, resulting in a warmer and much moister environment, as low-level moisture returns and the upper trough crosses just north of the region. This scenario will result in marginally unstable weather conditions and slightly cooler temperatures aloft. Therefore, expect a gradual transition to a wetter weather pattern with some instability aloft at least through Friday, with the potential for enhanced shower and isolated thunderstorm development across the islands and coastal waters. The potential for urban and small- stream flooding will increase, particularly during the afternoon hours. && .AVIATION...Mainly VFR conditions expected. However, SHRA with possible TSRA expected to develop along the Cordillera Central through 22Z. This activity is expected to reach TJSJ, with periods of reduced VIS and low ceilings. Winds will be out of the NE to E after 00Z, at 5 knots from the surface through FL080. Winds will pick up a bit after 12Z, out of the E at 8-10 kts. && .MARINE...Mariners can expect seas of 5 feet or less and winds out the east around 5 to 10 knots across the local waters. A small northeasterly swell spreading across the regional waters will promote a moderate risk of rip currents for most east- and north- facing beaches. Another small northerly swell and increasing winds up to 15 knots will yield life-threatening rip currents early next week. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && SHORT TERM...ERG PUBLIC DESK...GRS
Perspectivas sobre las Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia en San Juan PR 350 PM AST jueves 27 de abril de 2023 AMZ711>745-PRZ001>013-282000- 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 lejanas a la costa del Atlantico y del Caribe- 350 PM AST jueves 27 de abril de 2023 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Puerto Rico. .DIA UNO...Esta noche .Corrientes Marinas...Corrientes marinas amenazantes a la vida son posibles en la zona de las olas rompientes, particularmente en las playas del norte de Puerto Rico, Vieques, y Culebra. .DIAS DOS A SIETE...viernes a miercoles Se espera calor excesivo la mayoria de los dias a lo largo de la costa norte y oeste. Existe una probabilidad elevada de lluvia excesiva el viernes, pero el riesgo limitado existira en sectores del interior de la isla hasta mitad de semana. Se esperan tronadas aisladas el viernes y sabado. Se esperan vientos de 17 nudos o mas en el Atlantico cerca de las aguas costeras desde el lunes hasta el miercoles. Existe un riesgo moderado de corrientes marinas que persistira para la mayoria d elas playas con exposicion al norte y este. El lunes, un riego alto de corrientes marinas retornara para las playas con exposicion hacia el norte. .Comunicado sobre informacion reportada por observadores... No se necesita la activacion de observadores. AMZ716-726-VIZ001-002-282000- San Tomas, San John y las Islas Adyacentes-Santa Cruz-Aguas cercanas a la costa del Atlantico y aguas costeras adyacentes del Caribe- 350 PM AST jueves 27 de abril de 2023 Esta perspectiva sobre las condiciones peligrosas del tiempo es para las Islas Virgenes Estadounidenses. .DIA UNO...Hoy y esta noche .Corrientes Marinas...Es probable que se experimenten corrientes marinas amenazantes a la vida en la zona de las olas rompientes, particularmente en las playas del noroeste de San Thomas y el este de Santa Cruz. .DIAS DOS A SIETE...viernes a miercoles Un riesgo moderado corrientes marinas amenazantes a la vida persistira durante la semana laboral hasta temprano la proxima semana. .Comunicado sobre informacion reportada por observadores... No se necesita la activacion de observadores.
The San Juan radar (TJUA), 25 km away, was scanning. The volume nearest the first event began at 08:01 UTC.
7 flood, 5 flash flood, 3 debris flow, 1 thunderstorm wind. Local standard time, as filed.
A mudslide was reported in Sector Tarzan in Bayamon.
Mudslide was reported along road PR-606, just after Iglesia San Pedro and San Pablo.
Emergency managers reported flooding at Calle Georgetti, which is the road opposite to the Municipal Police Station.
Emergency managers reported five people trapped by a water surge in Charco La Buruquena. They were eventually rescued once the water levels receded.
Flooding was reported at Road PR-833, heading toward the park.
Water from flooding was entering into a house. The house was described as a pink house on the left of Cuesta La Cuertel.
Emergency managers reported a mudslide affecting road PR-830.
Emergency managers reported a tree down at road PR-815 in Naranjito. Wind speeds were around 25 mph.
Flooding was reported along Ave. Glasgow.
Flooding was reported along Calle 20.
Flooding was reported along Calle 21.
Significant flooding was reported along road PR-177, near Panderia Lemy.
A video shared by an employee from the NWS showed impassable roads near Ave. San Patricio.
A Grand Cherokee car was being swept by the flash flood near San Patricio, close to Church's Chicken fast food restaurant, and Oriental Bank.
NWS Employee reported about half a foot of standing water along Calle Dalia in Isla Verde. The road was still passable in some areas.
NWS employee indicated that the entrance to the gate to the Coco Beach living complex was impassable due to flooding.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2023Every state in 2023This day in weather historyWarnings in Puerto Rico, April 2023
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: 1085609, 1085608, 1085590, 1085591, 1085593, 1085594, 1085607, 1085597, 1085599, 1085600, 1085601, 1085602, 1085603, 1085604, 1085605, 1085606.