Strong diurnal heating and local effects combined with abundant low to mid-level moisture resulted in the development of heavy showers and thunderstorms across interior and western PR.
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The episode as NWS SJU wrote it up.
Strong diurnal heating and local effects combined with abundant low to mid-level moisture resulted in the development of heavy showers and thunderstorms across interior and 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 Jul 29, 10:31 AM AST, 5 hours 19 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 1031 AM AST Sat Jul 29 2017 .UPDATE...The weak tropical wave that moved across the region yesterday is now across Hispaniola. A relatively drier air mass moved across the local islands overnight and early this morning. A persistent but weakening upper level trough is expected to remain northeast of the region until tonight. An area of low level moisture embedded in the east southeast trade wind flow is expected to reach the local islands late this morning through at least Sunday morning. At this time, Doppler radar indicated isolated to scattered shower activity moving across the U.S. Virgin Islands, eastern sections of Puerto Rico as well as across the surrounding coastal waters. This activity was associated with the aforementioned surge of low level moisture. Not significant precipitation was observed elsewhere over land areas so far this morning. The surge of low level moisture in combination with the upper trough, strong daytime heating and local effects will be sufficient to produce the development of another round of scattered showers and isolated to scattered thunderstorms mostly along, north and northwest of Cordillera Central this afternoon. Due to previous days rainfall across these same areas, urban and small stream flooding are expected this afternoon. Showers and thunderstorms are also possible across the San Juan metro area. && .AVIATION...After 29/16Z, showers and thunderstorms are expected to increase across PR which is expected to cause at least VCTS across the terminals in PR and possible TEMPO TSRA at TJMZ and TJBQ at some point between 29/16Z and 29/21Z. Winds will be generally from the ESE at about 10-15KT today with sea breeze variations. Winds are expected to become light and variable after 29/22Z. && .MARINE...Relatively tranquil marine conditions are expected to continue during the rest of the weekend with winds at 10 to 15 knots and seas at 2 to 5 feet. A wind surge will increase seas and winds through much of next week, resulting in possible small craft advisories across the offshore waters and passages. && .PREV DISCUSSION... /issued 522 AM AST Sat Jul 29 2017/ SYNOPSIS... A TUTT low to the northeast will continue to move away as a mid to upper level ridge continues to build over the region. At the surface, a strong high pressure will continue to produce a east to east-southeast wind flow until Tuesday. A wind surge is forecast to arrive Monday afternoon into Tuesday ahead of the next tropical wave, which is forecast to arrive by Wednesday. SHORT TERM...Today through Monday... Brief showers are expected to continue affecting the local waters and portions of the USVI as well as eastern PR through the morning hours. An increase in available moisture is expected by this afternoon, which will help in the development of showers and thunderstorms in the afternoon hours when combined with the local effects. The most persistent showers and thunderstorms are expected to be across the western, interior, and northwestern sections of PR, but there is still a chance of showers and thunderstorms across other sections of the northern half of PR, including the San Juan metro. Temperatures across the lower elevations are expected to be hot, with max temps reaching the low to mid 90s and apparent temps likely surpassing 100 degrees for a few hours this afternoon. The higher elevations will not be as hot, with temps staying mainly in the low to mid 80s. Drier air is expected to move in on Sunday, which will cause a decrease in shower activity but there will still be a chance of showers and thunderstorms across the northwestern sections of PR due to the southeasterly wind flow. Then on Monday, the afternoon convection will possibly be more across western and central PR because the winds will be more easterly. LONG TERM...Tuesday through Sunday... A ridge aloft is expected to hold over the region the upcoming week. Under this pattern aloft the trade winds will push a Saharan Dust Particles over the islands. Also, a wind surge is forecast to increase winds across the islands by Tuesday ahead of the next tropical wave. Then, model guidance quickly bring a tropical wave with abundant tropical moisture Wednesday into early Thursday. This scenario can increase the potential for showers and thunderstorms across the islands. Moisture is forecast to rapidly erodes by Thursday afternoon or Friday, as another dry air mass with more Saharan dust particles filters over the islands. Saturday into Sunday, model guidance suggest an upper level trough over the islands with the arrival of another tropical wave by late Saturday or Sunday. The greatest shower coverage seems to be Wednesday into early Thursday. However each day the seasonable weather pattern can be expected across the region, with passing showers across the E-Puerto Rico and the U.S. Virgin Islands during the overnight and early morning hours followed by afternoon convection along and to the west of the Cordillera Central. AVIATION... VFR conds expected through 29/16Z with only VCSH until then across the local terminals except for TJMZ. Afternoon convection is expected across PR which is expected to cause at least VCTS across the terminals in PR and possible TEMPO TSRA at TJMZ and TJBQ at some point between 29/16Z and 29/21Z. Winds will be generally from the ESE at about 10-15KT today with sea breeze variations. MARINE... MARINE UPDATE...Fairly tranquil marine conditions are expected to continue during the weekend with winds at 10 to 15 knots and seas at 2 to 5 feet. A wind surge will increase seas and winds through much of next week. Resulting in possible small craft advisories across the offshore waters and passages. && .PRELIMINARY POINT TEMPS/POPS... SJU 90 80 91 81 / 50 30 30 20 STT 90 82 90 81 / 40 40 30 30 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && SHORT TERM...JF LONG TERM....99
Perspectivas sobre condiciones peligrosas del tiempo Servicio Nacional de Meteorologia San Juan PR 519 AM AST sabado 29 de julio de 2017 AMZ710>745-PRZ001>013-301000- 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- 519 AM AST sabado 29 de julio de 2017 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 posibilidad de tronadas con fuertes lluvias y vientos en rafagas breves esta tarde a traves de la mitad norte de Puerto Rico, con los aguaceros y tronadas mas persistentes posiblemente a traves de sectores del oeste, interior y noroeste de Puerto Rico al igual que sobre porciones del area metropolitana de San Juan. .Inundaciones...Se esperan que los aguaceros y tronadas podrian resultar en fuertes lluvias, que pudieran resultar en inundaciones urbanas y de riachuelos. .Corrientes marinas...Existe un riesgo moderado de corrientes marinas para las playas del norte central de Puerto Rico. .Calor...Vientos alisios del este sureste resultaran en temperaturas sobre lo normal y indice de calor a lo largo de las areas mas bajas de Puerto Rico. .Dias dos a siete...domingo a viernes Temperaturas maximas estaran sobre lo normal a traves de las areas mas bajas de Puerto Rico hasta por lo menos el lunes. Se espera una onda tropical el miercoles, que traera humedad adicional y posibles tronadas hacia el area local. Por lo menos un riesgo moderado de corrientes marinas se espera durante los proximos dias. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion generalizada de observadores, sin embargo, se exhorta a los observados a reportar inundaciones a la oficina del Servicio Nacional de Meteorologia en San Juan. AMZ715-725-VIZ001-002-301000- San Tomas, San John e islas adyacentes-Santa Cruz- Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe- 519 AM AST sabado 29 de julio de 2017 Esta perspectiva sobre las condiciones del tiempo peligrosas es para Puerto Rico y las aguas costeras adyacentes del Atlantico. .Dia uno...Hoy y Esta noche No es esperan condiciones peligrosas de tiempo en este momento. .Dias dos a siete...domingo a viernes Se espera una onda tropical el miercoles, que traera humedad adicional y posibles tronadas hacia el area local. Por lo menos un riesgo moderado de corrientes marinas se espera comenzando el lunes y los dias despues. .Comunicado sobre informacion reportada por observadores... No se anticipa activacion de observadores.
Special Weather Statement
National Weather Service San Juan PR
245 PM AST SAT JUL 29 2017
PRZ001-005-006-008>010-291945-
Northwest-San Juan and Vicinity-North Central-Central
Interior-Mayaguez and Vicinity-Western Interior-
245 PM AST SAT JUL 29 2017
...AN AREA OF THUNDERSTORMS WILL AFFECT LARES...MOROVIS...
NARANJITO...VEGA ALTA...SAN SEBASTIAN...ARECIBO...TOA BAJA...
ISABELA...MOCA...QUEBRADILLAS...RINCON...CIALES...HATILLO...UTUADO...
MANATI...FLORIDA...ANASCO...VEGA BAJA...CAMUY...BARCELONETA...
DORADO...COROZAL...AGUADA...AGUADILLA AND TOA ALTA MUNICIPALITIES...
At 241 PM AST, thunderstorms with frequent lightning were over
central and western Puerto Rico. These thunderstorms are
particularly dangerous because lightning is striking well outside
of the rain areas on the northern coastal plains from the
overhanging anvils of the storms.
Those outside should find lightning-safe shelter--inside--not under
trees.
LAT...LON 1850 6700 1848 6692 1849 6680 1847 6674
1849 6667 1848 6652 1847 6647 1848 6644
1847 6624 1831 6623 1831 6724 1835 6726
1837 6724 1842 6716 1848 6717 1851 6714
TIME...MOT...LOC 1841Z 240DEG 0KT 1845 6680
SnellComunicado Especial sobre las Condiciones del Tiempo Servicio Nacional de Meteorologia San Juan PR 245 PM AST sabado 29 de julio de 2017 PRZ001-005-006-008>010-2JFIGUEROA/ICOLONPAGAN91945-Noroeste-San Juan y Vecindad-Norte Central-Central Interior-Mayaguez y Vecindad-Oeste Interior-245 PM AST sabado 29 de julio de 2017 ...UN AREA DE FUERTES TRONADAS AFECTARA LOS SIGUIENTES MUNICIPIOS DE PUERTO RICO...LARES...MOROVIS...NARANJITO...VEGA ALTA...SAN SEBASTIAN...ARECIBO...TOA BAJA... ISABELA...MOCA...QUEBRADILLAS... RINCON... CIALES... HATILLO...UTUADO...MANATI...FLORIDA...ANASCO... VEGA BAJA...CAMUY...BARCELONETA...DORADO...COROZAL...AGUADA... AGUADILLA Y TOA ALTA... A las 2:41 PM AST, tronadas con actividad de rayos frecuente estaban localizadas sobre el centro y oeste de Puerto Rico. Estas tronadas son particularmente peligrosas ya que se han observado impactos de rayos fuera del area de lluvias a traves de las planicies costeras del norte. Aquellos que se encuentren al aire libre deben encontrar un lugar seguro dentro y no bajo arboles. Snell/ICOLONPAGAN
The San Juan radar (TJUA), 89 km away, was scanning. The volume nearest the first event began at 19:51 UTC.
1 flash flood. Local standard time, as filed.
Emergency management officials reported that a bridge was closed due to flooding from Rio Guajataca in Barrio Seburuquillo.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2017Every state in 2017This day in weather historyWarnings in Puerto Rico, July 2017
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: 715891.