Sufficient low-level moisture combined with strong daytime heating and local effects to generate showers and thunderstorms across portions of northern Puerto Rico as the steering flow was from the south.
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The episode as NWS SJU wrote it up.
Sufficient low-level moisture combined with strong daytime heating and local effects to generate showers and thunderstorms across portions of northern Puerto Rico as the steering flow was from the south.
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 30, 1:17 PM AST, 13 minutes earlier.
Area Forecast Discussion
National Weather Service San Juan PR
117 PM AST Mon Sep 30 2019
.SYNOPSIS...
There remains lingering moisture over the islands this afternoon,
aiding in the development of showers and isolated thunderstorms due
to local effects and daytime heating, especially in northern
portions of Puerto Rico. Increasingly dry conditions are anticipated
tomorrow through Thursday. Late on Friday, a weak tropical wave is
forecast to push into the forecast area, followed by a somewhat
stronger one on Sunday and another likely arriving on Tuesday next
week.
&&
.SHORT TERM...Today through Wednesday...
Showers and isolated thunderstorms are expected for this afternoon,
largely in northern and northwestern Puerto Rico in a generally
southerly wind flow, caused by local effects and daytime heating.
Some of these showers have already begun to develop, most notably
in north central portions of the island. Drying conditions will
be seen tomorrow through Thursday. That being said, there is
likely to be sufficient moisture in lower levels to fuel the
development of afternoon convective activity. With the mean flow
being out of the south/southeast over the next few days, the area
with the highest potential for showers and isolated thunderstorms
associated with this activity will remain to be northern and
northeastern Puerto Rico. The drier air aloft is forecast to
somewhat suppress this activity and rainfall amounts will be
generally lower compared to that of the previous days.
Warmer than average temperatures are possible, especially in
northern coastal areas, as warmer air from the south influences the
islands. The drier conditions will also likely serve to increase
daytime heating. Heat indices in the low 100s are possible.
.LONG TERM...Thursday through Tuesday... From Prev Discussion...
Southeast flow on Thursday at lower levels will bring drier air at
first, then a weak easterly wave with a patch of moisture will come
through on Friday. On Saturday moisture increases again, until the
next and more significant tropical wave moves through the area on
Sunday. Drying on Monday will be followed by even better moisture on
Tuesday with another tropical wave. At upper levels, low pressure
will move west into the Caribbean while higher pressure is draped
across the western Atlantic just north of Puerto Rico. The high and
the low will both move west and away from the area Friday and
Saturday leaving northeast flow over the area. That flow will
continue through Tuesday as a strong TUTT low approaches the
Caribbean on Sunday but weakens before moving across on Tuesday.
Models show enhanced divergence on Sunday afternoon with the passage
of the first significant tropical wave.
At this time the driest period looks to be Wednesday and Thursday,
while Saturday and Sunday and possibly the Tuesday after next will
have the best moisture for shower and thunderstorm activity. Mid
level temperatures will also decrease a degree or two Sunday through
Tuesday to add some extra instability.
&&
.AVIATION...Mainly VFR conditions are expected to prevail across
all terminals during the next 24 hours. However, SHRA/TSRA may
cause tempo MVFR conds thru 22z at TJBQ/TJSJ. Low level winds will
continue from the south between 10-15 kts, bcmg light and
variable overnight at the sfc.
&&
.MARINE...
Seas continue to subside in the Atlantic waters this afternoon, as
the effects of swells off of Hurricane Lorenzo diminish. For the
rest of today and tomorrow, seas up to around 6-6.5 feet are
possible, with further decreases expected during the second half of
the week. Elsewhere, relatively tranquil marine conditions will
continue through the week; wave heights in the Caribbean waters will
be up to around 3-6 feet.
Rip current will remain a concern on local beaches. There is a low
to moderate risk this afternoon in the U.S. Virgin Islands as well
as Vieques and Culebra. Southeastern Puerto Rico has a moderate risk
of rip currents, while north-facing beaches will have a moderate to
high risk.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 78 93 78 92 / 10 20 10 20
STT 81 88 80 88 / 10 10 10 10
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from Tuesday morning through Tuesday
afternoon for Northeast-Southeast.
High Rip Current Risk from 6 PM AST this evening through Tuesday
afternoon for North Central-San Juan and Vicinity.
High Rip Current Risk through Tuesday afternoon for Northwest.
VI...None.
AM...None.
&&
SHORT TERM...DS
LONG TERM....CRSPerspectivas sobre Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia San Juan PR 438 AM AST lunes 30 de septiembre de 2019 AMZ710>745-PRZ001>013-010845- 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 mar afuera del Atlantico y Caribe- 438 AM AST lunes 30 de septiembre de 2019 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 una probabilidad de tronadas con relampagos, lluvia fuerte y vientos en rafagas son posibles a traves del noroeste de Puerto Rico. .Inundaciones...Lluvia de moderada a fuerte pudiera causar acumulacion de agua en carreteras y en lugares de poco drenaje .Oleaje...Se espera oleaje de hasta 7 pies a traves de las aguas del mar afuera del Atlantico durante esta manana. A traves del este de las aguas del Atlantco, se espera oleaje de hasta 6 pies. .Corrientes Marinas...Existe un riesgo alto de corrientes marinas para las playas del noroeste de Puerto Rico. Se espera un riesgo alto de corrientes marinas a trves de la mayoria del las playas el norte para esta noche. .Calor...Temperaturas por encima de lo normal y alto contenido de humedad resultara en indices de calor entre 102 y 107 grados a traves de varaias areas bajas. .Dias dos hasta el siete...martes a domingo Se esperan idices de calor entre los 102 a 107 grados a traves de varias areas bajas. Un riesgo alto de corrientes marinas se espera para las playas del norte de Puerto Rico hasta el jueves. .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. AMZ715-725-VIZ001-002-010845- San Tomas, San John y Islas Adyacentes- Santa Cruz-Aguas cercanas del Atlantico y aguas costeras adyacente del Caribe- 438 AM AST lunes 30 de septiembre de 2019 .Dia Uno...Hoy y esta noche .Oleaje...Se espera oleaje picado de hasta 7 pies a traves de las aguas mar afuera del Atlantico esta manana. A traves del este de las aguas del Atlantco, se espera oleaje de hasta 6 pies. .Corrientes Marinas...Existe un riesgo moderado de corrientes marinas para la mayoria de las playas de Santa Cruz y las playas del sur de San Thomas y St. Jhon. .Dias dos hasta el siete...martes a domingo Se esperan idices de calor entre los 102 a 107 grados a traves de varias areas bajas. Un riesgo alto de corrientes marinas se espera para las playas del norte de Puerto Rico hasta el jueves. .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. Juan.
The San Juan radar (TJUA), 33 km away, was scanning. The volume nearest the first event began at 17:31 UTC.
1 tornado. Local standard time, as filed.
A short-lived tornado touched down in Sector La Cambija. A video of the event was recorded and put in social media.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2019Every state in 2019This day in weather historyThe tornado archive for Puerto Rico, 2019Warnings in Puerto Rico, September 2019
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: 857415.