A surge in low-level moisture combined with daytime heating and local effects to generate afternoon convection across the northwestern quadrant of PR. In addition, a persistent streamer developed from Trujillo Alto to Toa Baja, generating significant rainfall activity, especially across Toa Baja and Cata o, where estimates were in excess of 3-5 inches.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SJU wrote it up.
A surge in low-level moisture combined with daytime heating and local effects to generate afternoon convection across the northwestern quadrant of PR. In addition, a persistent streamer developed from Trujillo Alto to Toa Baja, generating significant rainfall activity, especially across Toa Baja and Cata o, where estimates were in excess of 3-5 inches.
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 Mar 20, 10:55 AM AST, 5 hours 5 minutes earlier.
Area Forecast Discussion
National Weather Service San Juan PR
1055 AM AST Sat Mar 20 2021
.UPDATE...
TJSJ 20/12z sounding revealed dry air and subsidence aloft. Also,
the region is under a northeast wind flow fluctuating between 7
and 15 knots in the first 2kft. The Precipitable Water is 1.09
inches, which is well below-normal for March. However, GOES-East
detected a patch of clouds and moisture approaching the islands.
Therefore, passing showers will continue affecting the windward
sections of PR/USVI and the local waters. Then, local effects,
diurnal heating, and sea breeze variations will aid in shower
activity across the interior and western sections of Puerto Rico
later this afternoon.
&&
.AVIATION...
VFR conditions will continue across most of the local terminals.
But a surge of moisture will bring BKN ceilings across NCM/KPK
thru at least 16z. Then, SHRA/-SHRA and clouds will increase
across E-PR/USVI and the interior and western portions of PR
between 20/16-23z. Winds will continue from the E/NE at 10-20
knots with higher gusts and sea breeze variations.
&&
.MARINE...
Mariners can expect seas up to 6 feet across the Offshore waters
and below 5 feet elsewhere. Winds will continue around 15 knots
but up to 20 knots across the Anegada Passage.
Beachgoers expect a high risk of rip currents across the north-
facing beaches of the Puerto Rico and Culebra.
&&
.PREV DISCUSSION... /issued 507 AM AST Sat Mar 20 2021/
SYNOPSIS...High pressure at the surface will continue over the
central Atlantic ocean. At upper levels high pressure continues
over South America and the Caribbean sea, interrupted only by the
passage of a weak trough on Tuesday night and Wednesday. Moderate
to fresh easterly trade winds continue over the area for at least
the next 7 days.
SHORT TERM...Today through Monday...
Relatively stable weather is expected to prevail through most of the
short-term period as a result of ridging from the mid to upper
levels. The surface high pressure over the western Atlantic will
move eastward north of the region relaxing the pressure gradient and
slightly decreasing the wind flow pattern. Moisture is confined
between 1000 to 700 MB, local, and diurnal effects could produce a
few showers during Saturday Afternoon. Showers that do develop
during the weekend will be short-lived and produce light rainfall
amounts.
Model guidance suggest Sunday as the most active day of the short-
term period, as weak surface perturbation reaches the forecast area.
This feature will advect showers inland, mainly over portions of
northeastern Puerto Rico during the morning. Diurnally induced
showers are expected for portions of interior and western Puerto
Rico. By Monday, winds will become more from the east southeast.
Thus, low level moisture will combine with local effects to generate
showers over the northwestern third of Puerto Rico.
LONG TERM...Tuesday through Friday...
Moisture deepens in the area just as a short wave trough
approaches from the northwest at upper levels. This will generate
better showers in western Puerto rico during the afternoon with
some showers in eastern Puerto Rico Tuesday and Wednesday
mornings. 500 mb temperatures will fall to almost minus 10 degrees
Celsius Tuesday and also generate isolated thunderstorms over
western Puerto Rico during the afternoon. Flow around the high
pressure moving northeast in the western Atlantic at mid and low
levels pushes the moisture back toward the south, leaving a
pattern Thursday through Saturday consisting of scattered showers
in shallow patches of moisture riding in the easterly trade winds
over Puerto Rico and the U.S. Virgin Islands. Hence we can expect
isolated to scattered showers in the overnight and morning hours
in eastern Puerto Rico and over the waters around the U.S. Virgin
Islands, and scattered showers in the afternoons in western and
interior Puerto Rico for the remainder of the period.
AVIATION...Mainly VFR conditions will prevail across all terminals
during the next 24 hours. However afternoon SHRA are expected at
TJMZ/TJBQ, but no significant impacts to operations are
anticipated. East to northeast low-level winds will continue
through 22z at 15-25 kts, decreasing 10-15 kt overnight.
MARINE...Seas are diminishing and winds are forecast to be a few
knots less over the local waters today. Small craft advisory
conditions are not expected through Friday, but mariners will need
to exercise caution for the next few days. Winds will also
diminish some more after Sunday.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 86 73 86 73 / 30 20 20 30
STT 84 73 84 74 / 20 20 20 40
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for Northeast-
Northwest-Southeast.
High Rip Current Risk through late tonight for Culebra-North
Central-San Juan and Vicinity.
VI...None.
AM...None.
&&
SHORT TERM...CAM
LONG TERM....GLPerspectivas sobre Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia en San Juan PR 506 AM AST sabado 20 de marzo de 2021 AMZ710>745-PRZ001>013-210915- 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- 506 AM AST sabado 20 de marzo 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 .Viento...Se esperan vientos en exceso de 20 mph (17 nudos) a traves de algunas areas de las aguas del Atlantico. .Olas...Se espera oleaje picado de hasta 6 pies a traves de las aguas del Atlantico y el Pasaje de Mona. .Corrientes Marinas...Existe un riesgo alto de corrientes marinas para las playas del norte de Puerto Rico y Culebra. .Dias dos hasta el siete...domingo a viernes El riesgo de corrientes marinas sera limitado a moderado el domingo. El riesgo alto de corrientes marinas regresara a las playas del norte el lunes y martes. .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-VIZ001-002-210915- San Tomas, San John e Islas Adyacentes- Santa Cruz-Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 506 AM AST sabado 20 de marzo 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 .Viento...Se esperan vientos en exceso de 20 mph (17 nudos) a traves de algunas areas de las aguas del Atlantico. .Olas...Se espera oleaje picado hasta 6 pies a traves de las aguas del Atlantico y el Pasaje de Anegada. .Corrientes Marinas...Existe un riesgo moderado de corrientes marinas a traves de la mayoria de las playas locales. .Dias dos hasta el siete...domingo a viernes Se espera que el riesgo moderado de corrientes marinas continue para las playas del norte y este de las Islas Virgenes Estadounidenses. .Comunicado sobre informacion reportada por observadores... No se espera activacion amplia de observadores. Sin embargo, 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), 37 km away, was scanning. The volume nearest the first event began at 19:58 UTC.
7 flood, 4 flash flood. Local standard time, as filed.
Flooding reported along Calle Jazmin in Sector Candelaria Arenas.
Road PR-167 between the Mcdonalds and Econo Supermarket was completely closed due to flooding.
Calle Mariano Brau reported flooding, affecting two houses.
Calle Dolores Cruz in the Urbanization of Villa Marasol was reported flooded.
Avenida de Lago in Levittown was flooded. Road was closed for several hours.
Flooding reported along Calle Las Flores in Sector Campanilla.
Road PR-165 near second section of Levittown was completely closed due to flooding.
Flooding reported along Avenida Luis Pares Matos.
Emergency manager called to report a rescue of three people due to heavy rainfall and the Rio Cucharillas out of its banks in sector Reparto Paraiso.
Calle Wilson had flooding due to poor drainage and problems with the pump drainage system.
Heavy rains lead to minor flooding Calle Malasia.
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, March 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: 950882, 950883, 950884, 950885, 950886, 950888, 950889, 950890, 950891, 950892, 950893.