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Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
852 FXCA62 TJSJ 120936 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 536 AM AST Mon Aug 12 2024 .SYNOPSIS... Above normal moisture levels, the proximity of an upper-level trough, and local effects will result in overnight and early morning passing showers followed by afternoon showers with thunderstorm activity, mainly across the interior and western Puerto Rico through Tuesday. Then, the forecast for the rest of the week will be dominated by the Potential Tropical Cyclone Five. The system is expected to become a tropical depression later today or tonight. Under the current forecast track, the closest approach of this system will near (or over) the northern USVI early Wednesday morning. A Tropical Storm Watch and a Flash Flood Watch are now in effect for Puerto Rico and the U.S. Virgin Islands. The main threats associated with this system are flooding rains, landslides, windy or possible tropical storm conditions and hazardous coastal and marine conditions. && .SHORT TERM...Today through Wednesday... A Tropical Storm Watch has been issued for the U.S. Virgin Islands with additional watches to be required later today. The Potential Tropical Cyclone Five will bring tropical storm force winds and periods of heavy rain, with the potential for flash flooding and mudslides. Hazardous marine and coastal conditions are also expected, beginning as early as Tuesday Evening. First rainbands are so far forecast to arrive by Tuesday afternoon, becoming more frequent and heavier by Tuesday Evening and continuing through Wednesday morning. At 200 AM AST (0600 UTC), the disturbance was centered near latitude 14.3 North, Longitude 51.4 West. The system is moving toward the west-northwest near 23 mph (37 km/h) and this motion is expected to continue during the next couple of days. On the forecast track, the disturbance is expected to move across portions of the Leeward Islands on Tuesday and approach the U.S. and British Virgin Islands Tuesday evening. Recent satellite imagery as well as satellite derived precipitable water products and model guidance, all suggest a slight decrease in columnar moisture today in advance of the broad and elongated Potential Tropical Cyclone Five. This disturbance was now some 715 miles east southeast of the island of Antigua quickly moving west northwest. Presently the proximity of a TUTT lifting north of the region and a building upper high pressure east of the area, will aid in promoting overnight and early morning showers across portions of the north and east sectors of the islands, as winds become more east northeast. Local sea breeze convergence, diurnal heating, local orographic effects, will therefore promote afternoon showers and possibly isolated thunderstorms, particularly across the interior and west to southwest sections of Puerto Rico. For the U.S. Virgin Islands, mainly passing showers driven by the wind flow are expect to continue with some reaching some of the islands at times. By Tuesday through Wednesday, with the increasing northeast winds, expect more frequent passing showers during the overnight and morning hours with also increased potential for more widespread afternoon and evening showers and thunderstorms with the approach of the aforementioned tropical Potential tropical cyclone Five. Current model guidance and the current NHC forecast track has PWAT values rapidly increasing late Tuesday through the rest of the period, as the disturbance and its associated outer bands approach and increase in frequency across the easternmost section of Puerto Rico as well as the U.S. Virgin Islands by the end of the period. By then the potential for excessive rainfall and flooding rains will increase as well as rapid rises along rivers and streams and potential for mudslides and rockfall in higher elevations of Puerto Rico. Tropical force winds and/or wind gusts will also be likely during the latter part of the period for most of the forecast area. s Residents and visitors should continue to monitor the progress of this system and review their tropical emergency plans.Please refer to the latest Tropical Cyclone Bulletin (TCPAT5) issued by National Hurricane Center and Hurricane Local Statements (HLSSJU) issued by WFO San Juan PR for the most up to date information. && .LONG TERM...Thursday through Sunday... For the beginning of the long-term forecast, hazards will continue to depend on the potential impacts from the now Potential Tropical Cyclone Five, which is forecast to move west-northwestward across or near the region as a tropical storm. The main threats associated with this system are flooding rains, landslides, windy or possible tropical storm conditions and hazardous coastal and marine conditions. PTC Five should start to move away from the area on Thursday generating southerly winds. Residual moisture will continue to be driven by the wind flow into our region causing additional rain. Heavy rainfall may result in locally considerable flash flooding and mudslides in portions of the U.S. Virgin Islands Tuesday and Wednesday, and into Puerto Rico Wednesday through early Thursday. Weather conditions are expected to quickly improve at the end of the week as a drier-than-normal air mass, with pockets of low-level moisture, moves into the area and we switch to a more typical pattern. && .AVIATION... (06Z TAFS) Prevailing VFR conds during prd but with passing SHRA/Isold TSRA to continue over the regional waters and en route btw islands. Low level winds continue from the east and is expected to become more east northeast then northeasterly by end of period as winds increase due to the approaching of the Potential Tropical Cyclone Five. Sfc wnds calm to light and variable but becoming east to northeast 10 to 15 mph with ocnly hir gust up to 25 kts psbl. Passing shra may cause local mtn top obscurations over interior sections of PR and brief MVFR conds. Aftn SHRA/TSRA expected over central and west sections of PR 12/16Z with mostly Isold SHRA at the USVI terminals. && .MARINE... A surface high pressure across the North Atlantic will maintain moderate to locally fresh easterly winds, creating localized choppy conditions for small craft. Potential Tropical Cyclone Five, located 940 miles ESE of San Juan, is expected to move into the local waters by Tuesday evening into Wednesday as a tropical cyclone. However, marine conditions in our eastern Atlantic waters and the Anegada Passage could deteriorate as early as Tuesday morning. Further deterioration in marine and weather conditions is expected Wednesday through Thursday. && .BEACH FORECAST... Today, there is a moderate risk of rip currents across most beaches of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands. Similar conditions are anticipated tomorrow throughout the day, then marine and coastal conditions will start to deteriorate due to the approaching Potential Tropical Cyclone 5. As a result, high risk of rip currents could start tomorrow night. Please refer to the Surf Zone Forecast (SRFSJU) for more details about the forecast. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Tropical Storm Watch for PRZ001>013. Flood Watch from Tuesday evening through Thursday morning for PRZ001>013. VI...Tropical Storm Watch for VIZ001-002. Flood Watch from Tuesday evening through Thursday morning for VIZ001-002. AM...Tropical Storm Watch for AMZ711-712-716-723-726-733-735-741-742- 745. && $$ OMS/RAM/YZR/RVT