Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
325 FXCA62 TJSJ 011454 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 1054 AM AST Wed May 1 2024 .UPDATE... A variable weather pattern prevailed during the morning hours across the local region. The heaviest activity was observed over the southeastern sections of Puerto Rico. Due to the local effects and the available moisture, a wet pattern is forecast for the rest of the afternoon hours. Therefore, residents over the northwestern and San Juan Metro areas could expect moderate to heavy showers. From Friday into the rest of the weekend, a more wet and unsettled pattern is expected due to the arrival of an upper-level trough and plenty of moisture across the area. Therefore, A hydrologic Outlook was issued due to the elevated risk of flooding across most of the region. Given the saturated soils and the expected conditions, urban flooding and small stream flooding. Residents should stay tuned for further weather updates. && .HYDROLOGY... Deep moisture and instability provided from a upper level trough will bring periods of showers and thunderstorms across the local islands during the next several days, particularly on Friday and into the upcoming weekend. Based on the latest guidance, the most likely time period for the heaviest rainfall activity is Friday afternoon into Saturday. As a result, there is an increasing risk for ponding of water, flooding of urban areas, roads and small streams. Life threatening flash flooding and mudslides are possible as well. Given the some uncertainty, rainfall accumulations will be available for the next day or so. A Flash Flood Watch will likely be issued on Thursday. .AVIATION... (12Z) SHRA/TSRA will continue to affect most of the TAF sites for the rest of the afternoon. Ts in the mountains can result in ceilings at FL030 across the interior PR and TJBQ. VCTS cannot be ruled out at times during the fcst period but confidence not high enough to add them at this moment for most terminals result in MVFR conditions. && .PREV DISCUSSION... /issued 516 AM AST Wed May 1 2024/ SYNOPSIS... From today onwards, expect the instability and moisture levels to increase once again, as a mid to upper level trough lingers over the western Atlantic and moisture from the Caribbean is brought into the area by east to southeast winds. Marine conditions will remain hazardous through at least tomorrow. A High Risk of Rip Currents will continue across western, northern, and eastern coastline of Puerto Rico and Culebra. SHORT TERM...Today through Friday... Breezy conditions and scattered to locally numerous showers prevailed once again during the overnight hours. Observed rainfall amounts during the past 6 hours were from a quarter of an inch in Patillas to 1.20 inches in Vega Baja and less than a quarter of an inch across the U.S. Virgin Islands. Minimum temperatures were from the mid-to-upper 70s across coastal areas to the mid-60s across the higher elevations. Wind gusts were between 25-30 mph across the northeast coast of PR and between 23-26 mph in St. Croix and St. Thomas. The forecast remains on track during the short-term period as a wetter and unstable pattern will evolve as an upper-level trough approaches the area from the west and an induced surface trough develops north of the region. In response, moisture pooling and lighter winds can be expected, further enhancing shower and thunderstorm development across the local area. Due to already saturated soils, any brief period of heavy showers or persistent light rainfall could lead to urban and small stream flooding, localized flash flooding, and mudslides, particularly across the interior and the eastern half of Puerto Rico. Regardless, all the islands could experience brief periods of heavy showers during the next several days. Steering winds are still expected to shift further from the S/SW on Thursday and Friday, increasing the potential for showers across San Juan and its vicinity. Today, the W/NW quadrant of PR should see more shower and thunderstorm development during the afternoon than previous days as winds shift more from the east to southeast. Please continue to monitor the weather conditions and be alert for any possible issuance of flood products. High temperatures will remain in the mid-to-upper 80s along the coastal and urban areas and from the mid-to-upper 70s along the mountains and valleys. Minimum temperatures will range from the mid and upper 70s across coastal areas to the mid-60s in the higher elevations LONG TERM...Saturday through Tuesday... The long-term period continues to lean towards a wet and unstable weather pattern across Puerto Rico and the U.S. Virgin Islands. As mentioned in the previous discussion, this weather pattern should prevail as a surface trough and a perturbation over the northeastern Caribbean merge across the forecast area, allowing rainfall activity to be the dominant feature throughout the long- term period. On Saturday, the upper level, yet maxima, should remain to the north of the area. Nonetheless, winds around 60 knots will still reach the region. At this time, models suggest Saturday as the wettest and most unstable day of the period. The Precipitable Water (PW) models show values above two standard deviations by the early part of the weekend. The 500 mb temperatures also suggest values around -8 degrees Celsius on Saturday, meaning that there is potential for some isolated thunderstorm activity across Puerto Rico and the U.S. Virgin Islands. Despite the fact that Saturday looks like the most unstable day, we can not rule out rainy days for the rest of the period. The latest model guidance suggests enough moisture extending across all levels of the atmosphere through Tuesday, meaning that rainy days are ahead. This increase in moisture content is due to a broad patch of moisture or perturbation over the Caribbean that will be absorbed and brought into the area by a strong trough. We anticipate active afternoons each day with the potential increase in the frequency of showers and isolated thunderstorms. Overall, the main hazards from Saturday into Tuesday are the increased risk of flooding across the islands and the risk of mudslides, particularly in areas of steep terrain in Puerto Rico. Therefore, we encourage citizens and visitors to be aware of any additional updates in the forecast. AVIATION... (06z) TAFS SHRA/TSRA with max tops around FL300 were observed across the Caribbean waters, and increasing across the Atlantic coastal waters overnight. This activity should impact manly TJPS thru 01/13z with possible tempo MVFR to IFR conds. Across, TJSJ/TIST/TISX/TJBQ mostly VCSH and -SHRA at times expected with brief MVFR cigs. Mtn top obscd and BKN/OVC lyrs will continue across PR. TSRA could develop later this afternoon near TJBQ/TJSJ causing tempo MVFR to brief IFR conds. East winds at 13-17 kt with stronger gusts near showers. VCTS cannot be ruled out at times during the fcst period but confidence not high enough to add them at this moment for most terminals. MARINE... A surface high pressure extending from the western to central Atlantic will tighten the local pressure gradient, promoting moderate to locally fresh trade winds across the Northeast Caribbean through at least tomorrow. As a result, expect hazardous seas for small craft operators due to confused seas associated with the increasing winds and a northeasterly swell spreading across the local waters. An induced surface trough, north of the islands, will weaken the pressure gradient and winds will shift from the east to east- southeast by the latter part of the week. BEACH FORECAST... A northerly swell and strong winds are resulting in High Risk of Rip Currents across some of the local beaches. The High Risk for western Puerto Rico, St. Thomas and St. John will continue through Thursday morning, while for the northern, eastern PR, and Culebra should remain through Thursday afternoon. For more information and details about the latest forecast please refer to the Surf Zone Forecast (SRFSJU) and the Coastal Hazard Message product (CFWSJU). && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Thursday afternoon for PRZ001-002- 005-008-012. High Rip Current Risk through late tonight for PRZ010. VI...High Rip Current Risk through late tonight for VIZ001. AM...Small Craft Advisory until midnight AST tonight for AMZ711-712- 716. Small Craft Advisory until 6 PM AST this evening for AMZ723-741- 742. && $$ SHORT TERM...LIS PUBLIC...MRR