A strong upper-level jet, which produced divergence aloft, combined with sufficient low-level moisture and local and diurnal effects to produce strong showers and thunderstorms over the Cordillera Central.
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The episode as NWS SJU wrote it up.
A strong upper-level jet, which produced divergence aloft, combined with sufficient low-level moisture and local and diurnal effects to produce strong showers and thunderstorms over the Cordillera Central.
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 Nov 1, 11:51 AM AST, 2 hours 24 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 1151 AM AST Thu Nov 1 2018 .UPDATE...The morning weather was fair across the local islands as expected. However, satellite imagery indicates that cloudiness has steadily developed across the local islands, especially across the mountains of the USVI and PR. Showers have also started developing across isolated areas. This shower activity is expected to become numerous with possible thunderstorms across the interior into northwestern PR this afternoon. Scattered showers are expected elsewhere in PR and a few showers could affect western PR before they stream off. The showers and thunderstorms expected this afternoon across the interior and NW-PR could become heavy at times, which could cause urban and small stream flooding. && .AVIATION...VFR conds expected across the local terminals. VCTS possible at TJBQ and TJMZ after 01/17Z, VCSH across the rest of the local terminals this afternoon. Easterly winds of around 10kts with sea breeze variations expected today. && .MARINE...Seas of 2 to 5 feet expected across the local waters. Easterly winds between 10-15 knots expected. && .PREV DISCUSSION... /issued 430 AM AST Thu Nov 1 2018/ SYNOPSIS...There is a chance for showers and thunderstorms during the next several days as moisture increases, an old frontal boundary approaches the area, and an upper level trough moves across the area. SHORT TERM...Today through Saturday... Late in the evening showers and isolated thunderstorms developed over portions of the interior, and northern areas of Puerto Rico. These showers and isolated thunderstorms were enhanced by the subtropical jet which provided upper-level divergent. TJUA Dual Pol storm total accumulations shows rainfall totals ranged from 2 to 4 inches in the aforementioned areas. Due to the moderate to heavy rainfall several flood advisories were issued. Since then showers have weakened across the area, but some mid to upper level clouds remain. A rather stable weather pattern will transition to an unsettled weather pattern; produced by a weak trough to the north of Puerto Rico, as well as a strong subtropical jet that is forecast to continue across the region through Saturday. The Subtropical jet will provide sufficient upper level divergent aloft over portions of northern, interior and western areas Puerto Rico during the afternoon which will induce shower and thunderstorm development. However, showers are possible across the eastern areas of Puerto Rico and areas east during the morning hours. The unstable conditions are depicted by GFS which has 500 mb temperatures decreasing to minus 10 degrees C on Friday, as well as increasing lapse rates from 700 to 500 mb. Additionally, Galvez- davison index shows values of 25 today through early Friday, but values increase to 35 late friday afternoon until Saturday. Values of 25 to 35 means there is potential for scattered thunderstorms or shallow convection across the forecast area. Guidance suggest the best instability will be late Friday night into Saturday. However, this depends on the proximity of the trough to the Puerto Rico any deviation in the position could require a minor forecast change in thunderstorm coverage for some areas. At this time this forecast will follow recent guidance that shows the trough moving over Puerto Rico. More importantly moderate to heavy rainfall could cause urban and small stream flooding, therefore if you see flooded roadways or areas that are flooded remember to turn around don't drown. LONG TERM...Sunday through Friday... TUTT low across the central Atlantic and into the eastern Caribbean will hold through the forecast cycle. At lower levels, moderate east northeast winds will prevail through Wednesday becoming gentle by the end of the work week as an induced surface trough develops across the eastern Caribbean. Latest guidance suggested PW values remaining near normal values much of the forecast period except on Tuesday when is expected to be slightly below the normal range. Long term forecast is highly dependent on the exact location of the aformentioned TUTT and associated axis. At this time, best divergence aloft is expected Sun-Mon as well as Thu as the axis relocates west of the local islands. Therefore, organized convection likely to be observed Sun-Mon with a more seasonal weather Tue-Wed. By the end of the week, the chance for showers and thunderstorms increases once again. AVIATION...VFR conditions will prevail across all the terminals through 01/15Z then SHRA/VCTS are possible across the interior and western areas of PR through 01/22z. These SHRA/VCTS could cause brief MVFR conds due to +SHRA with conds clearing by 01/22Z . Sfc winds will be light and variable today. MARINE...Seas will continue between 3 and 5 feet across the Atlantic waters and local passages today, elsewhere between 2 and 4 feet. Winds will be out from the east at 5 to 15 knots. An old frontal boundary approaches the area Friday and Saturday. This will cause winds and seas to increase during the weekend as well as the chance for shower and thunderstorm activity. && .PRELIMINARY POINT TEMPS/POPS... SJU 88 77 88 78 / 40 40 60 60 STT 88 77 88 76 / 40 40 50 60 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && SHORT TERM...JA LONG TERM....99
Perspectivas sobre Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia San Juan PR 513 AM AST jueves 1 de noviembre de 2018 AMZ710>745-PRZ001>013-020915- 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 Caribe- 513 AM AST jueves 1 de noviembre de 2018 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 la probabilidad de tronadas con lluvia fuerte y vientos en rafagas esta tarde a traves de porciones del este, interior y oeste de Puerto Rico. .Inundaciones...Lluvia de moderada a fuerte pudiera resultar en inundaciones urbanas y de riachuelos. .Corrientes marinas...Existe un riesgo moderado de corrientes marinas para la costa norte de Puerto Rico y la costa este de Culebra. .Dias dos a siete...viernes a miercoles Riesgo moderado de corrientes marinas continuara a traves de las playas orientadas al norte durante los proximos dias. Aguaceros y tronadas continuaran debido a una vaguada que se acerca. Temprano la proxima semana a medida que la vaguada se aleje, aire mas seco entrara a la zona desde el norte. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion amplia de observadores, sin embargo, se les exhorta a los observadores individuales a reportar inundaciones y corrientes marinas al Servicio Nacional de Meteorologia en San Juan. AMZ715-725-VIZ001-002-020915- San Tomas, San John e Islas Adyacentes- Santa Cruz- Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 513 AM AST jueves 1 de noviembre de 2018 Esta perspectiva sobre las condiciones del tiempo peligrosas es para las Islas Virgenes Americanas y las aguas costeras adyacentes. .Dia Uno...Hoy y esta noche .Corrientes marinas...Existe riesgo moderado de corrientes marinas para las playas de la costa norte, este y sureste de Santa Cruz. En San Tomas existe un riesgo moderado a traves de las playas del norte. .Dias dos a siete...viernes a miercoles Riesgo de moderado a alto de corrientes marinas continuara a traves de las islas locales, pero en particular en Santa Cruz durante los proximos dias. La probabilidad de lluvia y tronadas aumentara tarde esta semana al fin de semana. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion amplia de observadores, sin embargo, se les exhorta a los observadores individuales a reportar corrientes marinas al Servicio Nacional de Meteorologia en San Juan.
The San Juan radar (TJUA), 49 km away, was scanning. The volume nearest the first event began at 18:16 UTC.
2 hail, 2 thunderstorm wind. Local standard time, as filed.
Hail was reported in Barrio Cordillera along PR-146 near Escuela Superior Juan Antonio Corretjer.
Hail was reported in Barrio Pesas along Road PR-149 along the vicinity of Casona Bella Vista, a Gulf Gas Station, and Fussion Restaurant.
Strong wind gusts were reported in Barrio Cordillera along Road PR-146 near Escuela Superior Juan Antonio Corretjer.
Strong wind gusts downed trees and powerlines in Barrio Pesas along Road PR-149 near the vicinity of Casona Bella Vista, a Gulf Gas station and Fussion Restaurant.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2018Every state in 2018This day in weather historyWarnings in Puerto Rico, November 2018
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 2026-10-01. Each event’s entry at NCEI: 791986, 791995, 792010, 792013.