Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
224 FXCA62 TJSJ 112218 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 618 PM AST Sun Aug 11 2024 .SYNOPSIS... Invest 98L has now been designated Potential Tropical Cyclone Five. Under the current forecast track the closest approach of this system will near (or over) the northern USVI early Wednesday morning. The main threats associated with this system as it moves through late Tuesday into Wednesday are flooding rains, landslides, windy or possible tropical storm conditions and hazardous coastal and marine conditions. Tropical Cyclone Watches maybe required later tonight or early tomorrow. && .SHORT TERM...Tonight through Tuesday... Southeasterly steering flow, helped steer shower activity across most of Puerto Rico, with lines of showers developing northwest of the USVI, El Yunque and the central mountain range during the late morning to afternoon hours. THe strongest activity with thunderstorms converged over interior to northwestern PR, and prompted the issuance of a Special Weather Statement and a Flood Advisory over northwestern municipalities. Another flood product was issued for several metropolitan area municipalities due to the line from El Yunque. This shower activity at least brought some relief in terms of heat to the northwestern quadrant. Official and unofficial stations in St. Croix, north-central PR and southwestern PR reported heat indices above 108 at around 14:30 AST. Radar estimated accumulations around/above 2 inches were observed at Jayuya, Moca, Aguada, Naguabo and San Juan. San Juan, particularly Santurce, saw radar estimated accumulations of up to around 4 inches. Westernmost St. Thomas saw radar estimated accumulations of up to 0.16 in, the most in the USVI. Current satellite derived precipitable water (PWAT) values indicate around high end normal to above normal (above 2.0 inches) values across most of the values. The USVI had around 1.88 inches of PWAT values. Columnar moisture is forecast to slightly decrease to normal values tomorrow, Monday. A TUTT near the area will promote increased night showers tonight across windward sectors of the islands as winds become more easterly. Sea breeze convergence, diurnal heating, local orographic effects, and the aforementioned features will promote afternoon activity on Monday. Afternoon showers and isolated thunderstorm activity are expected across the interior and western Puerto Rico. For the U.S. Virgin Islands, mainly passing showers driven by the wind flow will reach the area at times through early Tuesday. Through Tuesday afternoon, a similar pattern will persist with high heat indices and afternoon showers and thunderstorms concentrating over western Puerto Rico. Current model guidance and the current NHC forecast track has PWAT values rapidly increasing late Tuesday to end the forecast period as the now Potential Tropical Cyclone Five and possible outer bands approach the easternmost region to end the period. Residents and visitors should continue to monitor the progress of this system and review their tropical emergency plans. .LONG TERM...Wednesday through Saturday... Long-term forecast hazards will 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 cyclone Tuesday night into Wednesday. A tropical cyclone watch or warning has not been issued at the time of this product for Puerto Rico and the USVI, as it is still early. However, we may need to issue a watch later tonight or early tomorrow. However, given the latest forecast track and intensity, now is an opportune moment to initiate preparatory measures for a potential direct or indirect impact from this system. The main threats associated with this system are flooding rains, landslides, windy or possible tropical storm conditions and hazardous coastal and marine conditions. Under the current forecast track the closest approach of this system will near (or over) the northern USVI early Wednesday morning. Weather conditions are expected to improve quickly later in the week as a drier-than- normal air mass, with pockets of low- level moisture, moves into the area. && .AVIATION... (18Z TAFS) Flow is now east southeast at 10 to 16 knots. Current SHRA/TSRA will diminish ovr PR aft 11/22Z, and winds will diminish to 5-10 kt, but SHRA activity ovr the local waters, arnd the USVI, and the SE third of PR will cont thru the pd, with lcl mtn obscurations and MVFR conds. Outlook: SHRA/TSRA to redevelop aft 12/15Z ovr PR. && .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 950 miles ESE of Antigua is expected to move into the local waters Tuesday afternoon and 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 are expected Wednesday and Thursday. && .BEACH FORECAST... Tonight, there is a moderate risk of rip currents on beaches of northern, southeastern and southwestern Puerto Rico and Saint Croix, extending to Culebra and Vieques tomorrow. Overall, the risk of rip currents could start to increase to high starting tomorrow night. Please refer to the Surf Zone Forecast (SRFSJU) for more information. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ CAM/MRR/GRS/WS/ERF/EM