Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
951 FXCA62 TJSJ 042118 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 518 PM AST Sat May 4 2024 .SYNOPSIS... A Flood Watch remains in effect for all Puerto Rico and the U.S. Virgin Islands, with saturated soils, any brief period of heavy showers or persistentlight rain could lead to urban andsmall- streamflooding, localized flashflooding, and debris flow. The precipitable water content is forecast to remain above normal levels through most of the forecast period, with a drying trend anticipated late next week. && .SHORT TERM...Tonight through Monday... The subsidence side of the trough that has been affecting the region this week worked against afternoon local effect induced convective activity. Limited afternoon convection affected sectors of SW Puerto Rico, western interior to north-central, and the metropolitan area. As of 440 PM AST, the highest radar estimated accumulations, around an inch, due to afternoon convection were observed over sectors of Utuado, Lares, San Sebastian, Arecibo. Highs were in the upper 80s to low 90s across coastal areas of the islands. Under light winds, showers will continue to affect sectors of the interior to north-central, and possibly the metro area this evening before gradually dissipating. Current satellite derived precipitable water (PWAT) values show the bulk of above normal values, above 2 inches, over the SE local offshore Caribbean Waters, St. Croix, and the Anegada Passage. Another area of up to 2 inches is over the northern coastline of Puerto Rico. Current model guidance indicate above normal PWAT values returning by late Sunday morning through the end of the forecast period under more easterly- se surface flow. This will be in part due to a surface high pressure moving into the western Atlantic. A Saharan Air Layer continues to move over the Atlantic, reaching the eastern Caribbean this weekend but the bulk of this layer should stay to our south. Model guidance suggests some of the bulk of this layer reaching the area by the long term period. A Flood Watch continues to be in effect through tomorrow afternoon for the region, with saturated soils, any brief period of heavy showers or persistentlight rain could lead to urban andsmall- streamflooding, localized flashflooding, and debris flow. National Blend of Models suggests afternoon convection developing tomorrow, especially across PR`s central mountain range. .LONG TERM...Tuesday through Saturday... .FROM PREV DISCUSSION...Issued at 536 AM AST Sat May 4 2024/ By the beginning of the long-term period, the latest models are suggesting a surface high pressure dominating over the western to central Atlantic. In our area, this will promote light to moderate winds from the east to northeast through the end of the workweek. At upper levels, another trough will pass mainly to our northfrom Tuesday through Thursday, maintaining unstable conditionsacross the islands. A moist airmass should linger over the local as moisture from the tropics will be pulled and join the remnants of the previous surface trough. The Precipitable Water (PWAT) model guidance shows values above normal climatological levelsthrough at least next Thursday; values around 2.00-2.25 inches. Consequently, the wet pattern is expected to continue with daily showers and possible isolated thunderstorms development. Shower activity should develop during the morning hours over portions of eastern PR and USVI, followed by afternoon convection over central and western PR resulting in greater accumulations. We encourage residents and visitors to remain weather-aware because any additional shower activity over saturated soils will further enhance the potential for flash flooding and mudslides. On the bright side, more stable conditions are forecast by the end of the week into the weekend as a mid-level ridge over the western Caribbean extends into the local area, bringing a drier air mass into the region resulting in more seasonal PWAT values and decreasing the potential for showers development. && .AVIATION... (18Z TAFS) Passing SHRA will affect the area, causing mountain obscuration across the Cordillera Central through 22Z. Winds will shift from the ENE at the surface at 05/12Z, with VCSH expected for the USVI and TJSJ terminals. Another round of SHRA and TSRA expected tomorrow along the Cordillera Central after 17Z. Winds are expected from the ENE at 5-10 kts through 2000 ft, and from the SW from 2000-8000 ft. && .MARINE... An induced surface trough moving across our area will yield lighter winds, while promoting the possibility of shower and thunderstorm development through early next week. A surface high pressure extending from the western to central Atlantic will promote light to moderate trade winds across the regional waters through the forecast period. && .BEACH FORECAST... A fading northerly swell and light winds will promote low to moderate risk of rip currents during the next several days. However, life-threatening rip currents often occur in the vicinity of jetties, and piers. && .HYDROLOGY... A Flood Watch remains in effect for all of PR and the USVI from this morning through Sunday afternoon. Please refer to the latest Flood Watch (FFASJU) for more information. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Flood Watch through Sunday afternoon for PRZ001>013. VI...Flood Watch through Sunday afternoon for VIZ001-002. AM...None. && $$ SHORT TERM....ICP LONG TERM.....MRR PUBLIC DESK...GRS