A tropical wave moving across the region combined with strong daytime heating produced strong thunderstorm activity across the northern half of PR during the afternoon hours.
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The episode as NWS SJU wrote it up.
A tropical wave moving across the region combined with strong daytime heating produced strong thunderstorm activity across the northern half of PR during the afternoon hours.
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 Aug 11, 11:56 AM AST, 2 hours 19 minutes earlier.
Area Forecast Discussion National Weather Service San Juan PR 1156 AM AST Fri Aug 11 2017 .UPDATE...No change to inherited forecast package at this time. Little or no shower activity observed over the land areas during the morning hours as most of the shower activity was noted over the coastal waters. Expect increasing cloud cover along the interior sections of PR during the rest the morning and afternoon. Diurnally and locally induced convection can be expected along parts of the interior and mainly northern half of PR as well as over parts of the U.S Virgin Islands, especially around the island of Saint Croix during the afternoon. Some of this activity may possibly spread over the northern islands later in the evening and overnight, as moisture associated with a tropical wave will lift west northwest across the region. This additional moisture will aid in the development of shower activity as it interacts with the Tutt which is forecast to also move westward northwest and just north of the region through Saturday. && .AVIATION UPDATE...No change to previous AVN discussion. VFR conds to prevail durg entire. Expect cloudiness and showers with possibly an isolated thunderstorms mainly across the central mountain range of Puerto Rico, with periods of SHRA/isold TSRA VCTY TJSJ/TJMZ/TJBQ through 11/22Z. Low level winds will be mainly south southeast at 10-15 kts. Except for local sea breeze variations winds from the east southeast at 10 to 15 knots. && .MARINE UPDATE...No chg to previous marine discussion. Wind and seas to continue at 10 to 15 knots and 5 feet or less through the upcoming weekend. && .PREV DISCUSSION... /issued 430 AM AST Fri Aug 11 2017/ SYNOPSIS... A weak surface low northeast of the region and its associated tropical wave extending from the surface low across the northeast Caribbean this morning will continue to move west northwest today and tonight. The wave is being generated by an upper level trough that will remain in tandem with its movements. These features will increase the moisture across the forecast today and Saturday, but model guidance indicated that the bulk of the moisture is expected to pass mostly north of the region. SHORT TERM...Today through Sunday Scattered showers with isolated thunderstorms were observed mainly across the Atlantic waters overnight. Some of these showers moved across the north coast of Puerto Rico affecting mainly the municipalities of Arecibo, Hatillo and Camuy. Other showers affected the U.S. Virgin Islands from time to time. Rainfall accumulation was less than half inch. For this morning, some showers will affect the local islands but these showers will move quickly. For this afternoon, available moisture will combine with daytime heating and local effects to produce scattered to numerous showers with thunderstorms mainly across the northern half of Puerto Rico as surface winds shifts from a southeasterly to a more southerly component. Due to a southerly wind flow at the surface, warmer than normal temperatures are expected along the northern slopes of Puerto Rico. As a result, near record maximum temperatures can be expected. The record maximum temperature at the Luis Munoz Marin International airport for today is 92F set in 2011. For the weekend, a drier air mass is expected to encompass the region, which will result in slightly less shower activity across the region. LONG TERM...Monday through Friday... Patches of moisture embedded in the trades will move across the region on Monday, before a tropical wave moves over the northeast Caribbean Monday night into early Tuesday. This wave will increase the shower and thunderstorm activity across the forecast area. Model guidance suggests that after the passage of the wave, a large area of SAL, extending from near the surface all the way to mid levels is expected to encompass the region Tuesday through at least Wednesday. By that time, some moisture will be seen across the region especially in the afternoon across interior and western Puerto Rico in typical diurnal pattern, but not significant or widespread precipitation is expected. Another, but stronger tropical wave will move through the region Thursday and Friday. AVIATION...Mostly VFR conditions are expected to prevail across the local flying area until at least 11/16Z. Cloudiness and showers will gradually increase across mountain ranges of Puerto Rico, inducing periods of SHRA/TSRA in and around TJSJ, TJMZ and TJBQ through 11/22Z. Low level winds will be mainly south southeast at 10 kts. MARINE... Local buoys continued to indicate winds around 15 knots and seas at 6 feet or less diminishing to 3-5 feet by the weekend, remaining below SCA criteria. Model guidance suggest increasing seas and winds by the upcoming week as another tropical wave move by the islands on Tuesday. && .PRELIMINARY POINT TEMPS/POPS... SJU 91 79 92 80 / 50 30 30 30 STT 89 81 90 80 / 50 50 20 40 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && SHORT TERM...RAM LONG TERM....RAM
Hazardous Weather Outlook...CORRECTED National Weather Service San Juan PR 716 AM AST Fri Aug 11 2017 AMZ710>745-PRZ001>013-120945- San Juan and Vicinity-Northeast-Southeast-Eastern Interior- North Central-Central Interior-Ponce and Vicinity-Nortwest- Western Interior-Mayaguez and Vicinity-Southwest-Culebra-Vieques- The nearshore and off shore Atlantic and Caribbean Coastal Waters- 716 AM AST Fri Aug 11 2017 This Hazardous Weather Outlook is for Puerto Rico and the adjacent Atlantic Coastal Waters. .Day One...Today and Tonight .Thunderstorms...There is a chance of thunderstorms with heavy rainfall and brief gusty winds this afternoon across the northern half of Puerto Rico. .Flooding...Heavy rains could lead to urban and small stream flooding. .Wind...Sustained winds in excess of 20 MPH are possible across a sector of the near and offshore Atlantic waters. .Waves...Choppy seas up to 6 feet are expected across the offshore Atlantic waters. .Rip Currents...There is a moderate risk of rip currents for much of the northern coast and for a portion of the southeast coast of Puerto Rico as well for most beaches of Vieques and Culebra. .Heat...Southeasterly trade winds will result in above normal heat index along the north coast of Puerto Rico. .Days Two through Seven...Saturday through Thursday A moderate risk of rip currents is expected through most of the weekend. A High risk of rip current is possible by mid week as tropical wave is forecast to move across the region. .Spotter information statement... Widespread spotter activation is not anticipated, however individual spotter are encouraged to report Rip Currents to the National Weather Service in San Juan. AMZ715-725-VIZ001-002-120945- St. Thomas St. John adjacent Islands-St Croix- Nearshore Atlantic and adjacent Caribbean Coastal Waters- 716 AM AST Fri Aug 11 2017 This Hazardous Weather Outlook is for the U.S. Virgin Islands and the ADJACENT Coastal Waters. .Day One...Today and Tonight .Waves...Choppy seas up to 6 feet are expected across the offshore Atlantic waters. .Rip Currents...There is a moderate risk of rip currents for some of the beaches of northern Saint Croix. .Days Two through Seven...Saturday through Thursday There is a moderate risk of rip currents for some of the beaches of Saint Croix through the weekend. A tropical wave is forecast to move across the region by the middle of next week. .Spotter information statement... Widespread spotter activation is not anticipated, however individual spotter are encouraged to report Rip Currents to the National Weather Service in San Juan.
The San Juan radar (TJUA), 33 km away, was scanning. The volume nearest the first event began at 18:14 UTC.
3 funnel cloud, 2 thunderstorm wind. Local standard time, as filed.
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Tree fallen at Belmonte street in San Juan municipality.
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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, August 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: 718924, 718925, 718930, 718933, 718934.