An upper-level low near the region combined with sufficient low-level moisture to result in locally and diurnally induced shower activity across western PR.
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The episode as NWS SJU wrote it up.
An upper-level low near the region combined with sufficient low-level moisture to result in locally and diurnally induced shower activity across western PR.
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 Jun 25, 9:53 AM AST, 2 hours 42 minutes earlier.
Area Forecast Discussion
National Weather Service San Juan PR
953 AM AST Thu Jun 25 2020
.UPDATE...Sunny to partly cloudy skies prevailed with a slight
haze layer due to suspended Saharan dust. Passing showers were
noted across the USVI and eastern portions of PR, but no
significant rainfall amounts were observed. For the rest of the
day, diurnally induced showers and isolated thunderstorms are
expected to develop over the interior/western sections of PR and
from streamers developing off the USVI and eastern PR. Urban and
small stream flooding is possible with the thunderstorms this
afternoon. No change from previous forecast.
&&
.AVIATION...Mainly VFR conditions expected to prevail. However,
SHRA/TSRA expected over western PR which should cause tempo MVFR
at JMZ/JBQ, elsewhere, VCSH/VCTS possible through 22z. The 12z
TJSJ upper air sounding indicated East winds up to 28 kt below
FL100.
&&
.MARINE...Choppy seas will increase between 4-6 feet today to 7
feet tonight across portions of the offshore waters and passages.
Therefore, small craft advisories are in effect. Winds will
prevail between 15-20 knots with higher gusts. A moderate risk of
rip currents continues for most of the local beaches of the
islands.
&&
.PREV DISCUSSION... /issued 521 AM AST Thu Jun 25 2020/
SYNOPSIS...
Moisture associated with a tropical wave will move over the region
late today into Friday. An increase in shower and thunderstorm
activity is expected for the afternoon hours due to the local
effects. The heaviest showers with is expected mainly over western
sections of Puerto Rico, elsewhere isolated to scattered showers are
expected. On Friday, more rain activity is expected with the
tropical wave. A more dry airmass is forecast to reach the region
for the weekend and will produce less shower activity and more fair
weather conditions. A wind speed increase is expected over the local
waters resulting in choppy marine conditions with seas up to 7 feet
in the Atlantic and Caribbean waters as well the local passages.
SHORT TERM...Today through Saturday...
A slot of dry air will be moving in today across the local area,
causing a decrease in the shower activity through the mid morning
hours. However, the local effects will combine with the diurnal
heating and some instability from an upper-level low to cause
afternoon shower and thunderstorm activity. The most significant
shower activity will be across the western sections of Puerto Rico.
The Saharan dust concentration will continue to decrease today. For
Friday, a tropical wave will be moving in, which will cause a
significant increase in moisture and shower activity across the
local area. The latest model guidance suggests that the tropical
wave will move in the morning across the USVI and then over PR for
the afternoon hours. This tropical wave will also come in with a
surge in winds from the east, causing wind speeds to be near 20 mph.
This will could cause the shower and thunderstorm activity to move a
bit more inland across eastern PR and into the eastern interior
sections, though the high res models are not suggesting too much
rain, partly because of the fast moving showers. As far as the USVI,
the expectation is the same, where showers and thunderstorms are
expected, but may be brief as the showers could be moving quickly.
However, later in the afternoon, the shower activity will be more
significant for central and western PR. One thing to note is that
there will be an increase in Saharan dust on Friday, which could
inhibit some of the convection. Then on Saturday, a return of
relatively dry air is expected, with the presence of Saharan Dust,
though not as much as we observed early in the week, but shower
activity will be limited mainly to locally induced showers across
western PR.
LONG TERM...Sunday through Thursday
The long term period start with a more drier mass over the region
limiting the development of well convection specially in the
afternoon hours. This weather patter si expected through at least
on Monday when fragments of moisture reach the local area embedded
in a east northeasterly wind flow. This will enhance the chance
of rain activity in the central and southwestern sections of
Puerto Rico in the afternoon hours. Late Tuesday into Wednesday, a
tropical wave is expected to move over the region. This wave will
bring enough moisture to increase the shower well convective
development for at least Thursday. Therefore, isolated to
scattered showers are expected over eastern sections of Puerto
Rico and the U.S. Virgin Islands in the morning hours and the
afternoon convection over the interior sections and northwestern
quadrant of Puerto Rico. This weather pattern is expected for at
least Thursday.
AVIATION...
Aviation...
VFR conditions will prevail through 25/16Z with SCT SHRA across the
area, causing VCSH. After 25/16Z, VCTS could affect TJBQ, though
ISOL/SCT SHRA is expected elsewhere. Approaching tropical wave will
bring NMRS SHRA / ISOL TSRA to the local area after 26/06Z. Winds
will be from the East at 15 to 20 knots with occasional gusts after
25/13Z, but winds will remain around 10kt or so after 25/23Z. Some
Saharan dust is still present, therefore HZ could be observed, but
VIS is expected to be P6SM.
MARINE...
Moderate to fresh easterly wind flow will continue for at least
Friday late night resulting in choppy marine conditions with sea
up to 6 feet over the local water. Therefore, a small craft
advisory is effect from this evening to Saturday afternoon.There is
a moderate risk of rip currents for most Puerto Rican beaches
including Culebra and Vieques.Showers and isolated thunderstorms
are possible across the regional waters due to a tropical wave
forecast to move over the region today.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 80 89 79 / 20 60 60 20
STT 90 80 90 80 / 40 50 50 20
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...VI...None.
AM...Small Craft Advisory from 2 AM to 8 PM AST Friday for Anegada
Passage Southward to 17N.
Small Craft Advisory from 8 AM to 8 PM AST Friday for Coastal
Waters of Northern USVI and Culebra out 10 NM-Coastal
Waters of Southern USVI Vieques and Eastern Puerto Rico out
10 NM.
Small Craft Advisory from 8 PM this evening to 2 PM AST Saturday
for Caribbean Waters of Puerto Rico from 10 NM to 17N-
Atlantic Waters of Puerto Rico and USVI from 10 NM to 19.5N-
Mona Passage Southward to 17N.
&&
SHORT TERM...DS
LONG TERM....CS
PUBLIC DESK...GLPerspectivas sobre Condiciones Peligrosas del Tiempo Servicio Nacional de Meteorologia San Juan PR 453 AM AST jueves 25 de junio de 2020 AMZ710>745-PRZ001>013-261000- 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- 453 AM AST jueves 25de junio de 2020 Esta perspectiva sobre las condiciones peligrosas del tiempo es para Puerto Rico y las aguas costeras del Atlantico. .Dia Uno...Hoy y esta noche .Tronadas...Existe la probabilidad de tronadas con lluvias fuertes, vientos en rafagas, y relampagos frequentes esta tarde a traves de sectores del oeste de Puerto Rico. .Inundaciones...Lluvias fuertes pudieran causar inundaciones urbanas y de riachuelos pequenos. .Viento...Se anticipan vientos sostenidos en exceso de 20 MPH (17 nudos) a traves de las aguas locales del Atlantico y caribe. .Oleaje...Oleaje picado/peligroso de hasta 6 pies se espera, aumentando a 7 pies para esta noche a traves de las aguas mar afuera del Atlantico y del Caribe. .Corrientes Marinas...Existe un riesgo moderado de corrientes marinas para la mayoria de las playas locales. .Dias dos hasta el siete...viernes a miercoles Vientos vigorosos y condiciones maritimas peligrososas se observaran el viernes a medida que una onda tropical se mueva a atraves del area. Aguaceros numerosos y tronadas aisladas tambien afectaran el area local el viernes y podrian causar inundaciones urbanas y de pequenos riachuelos. Existe un riesgo moderado de corrientes marinas para la mayoria de las playas locales por los proximos dias. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion de observadores, sin embargo, se recomienda a los observadores individuales que reporten inundaciones, vientos, olas y corrientes marinas al Servicio Nacional de Meteorologia en San Juan mientras siguen las indicaciones de las autoridades locales y estatales. AMZ715-725-VIZ001-002-261000- San Tomas, San John y Islas Adyacentes-Santa Cruz- Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 453 AM AST jueves 25 de junio de 2020 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 anticipan vientos sostenidos en exceso de 20 MPH (17 nudos) a traves de las aguas del Atlantico. .Oleaje...Oleaje picado/peligroso de hasta 6 pies se espera, aumentando a 7 pies para esta noche a traves de las aguas mar afuera del Atlantico y del Caribe. .Corrientes Marinas...Existe un riesgo moderado de corrientes marinas para la mayoria de las playas locales .Dias dos hasta el siete...viernes a miercoles Vientos vigorosos y condiciones maritimas peligrososas se observaran el viernes a medida que una onda tropical se mueva a atraves del area. Aguaceros numerosos y tronadas aisladas tambien afectaran el area local el viernes y podrian causar inundaciones menores. Existe un riesgo moderado de corrientes marinas para la mayoria de las playas locales por los proximos dias. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion de observadores, sin embargo, se recomienda a los observadores individuales que reporten vientos, oleaje y corrientes marinas al Servicio Nacional de Meteorologia en San Juan mientras siguen las indicaciones de las autoridades locales y estatales.
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Urban flooding reported in Calle Nenadich with the intersection with Road PR-2R.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2020Every state in 2020This day in weather historyWarnings in Puerto Rico, June 2020
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: 905681.