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875 FXCA62 TJSJ 081946 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 346 PM AST Sun Sep 8 2024 .SYNOPSIS... Expect shower and thunderstorm activity during the next few days as the tropical upper tropospheric trough (TUTT) and a broad tropical wave continues to move across the area. Southeasterly winds and a high- moisture environment will also contribute to excessive heat risks. The National Hurricane Center (NHC) is monitoring an area, currently in the central tropical Atlantic, with a medium cyclonic formation chance in the next 48 hours and a high formation chance in the next seven days. && .SHORT TERM...Today through Tuesday... Doppler radar observed isolated shower activity across eastern Puerto Rico and the U.S. Virgin Islands in the morning. Around 10 AM, more well-developed showers began streaming across the eastern sections of Puerto Rico, affecting Luquillo, Rio Grande, and Fajardo. Afterward, the shower activity started to develop across most of the eastern sections of Puerto Rico, the interior, and the northwestern regions. Intense shower activity resulted in rainfall accumulations between 1 and 3 inches, with the highest amount observed in San Sebastian, where radar estimates indicated around 3 inches. Although cloud cover persisted throughout the morning, maximum temperatures climbed into the upper 80s to lower 90s, with heat indices ranging from 108 to 110 degrees particularly along the southern coastal areas. Unsettled and wet weather conditions will prevail for the rest of the forecast period. The upper-level low will continue to linger across the islands, resulting in an unstable pattern conducive to the development of showers. Meanwhile, at the surface, a tropical wave moving westward into the region will provide abundant moisture, with PWAT values of 2.1 inches as indicated by derived GOES satellite images. This combination will trigger active afternoon showers and variable weather conditions during the late and early morning hours. Given these expected conditions, the risk of excessive rainfall will remain elevated, mainly for Puerto Rico. Saturated soils could lead to localized flash flooding and mudslides, particularly in small streams, creeks, and areas of steep terrain. Residents and visitors should exercise caution or avoid outdoor activities during the afternoon. Across the U.S. Virgin Islands, minor flooding may occur on roads and in poor drainage areas as shower activity increases. Temperature-wise, the islands can expect warmer conditions, with maximum temperatures in the upper 80s to lower 90s across most urban and coastal areas. Heat indices could exacerbate health issues, particularly in vulnerable populations. Given the forecast conditions, heat advisories and warnings are likely to be issued. && .LONG TERM...Wednesday through Sunday... //from previous discussion// An upper level trough will be present northeast of the local islands to start the period, before gradually weakening throughout the workweek. By the end of the week, a mid-level ridge will reduce instability aloft. Precipitable water (PWAT) values will continue mainly above 2.1 inches for the start of the period, above normal values for this time of the year. East to east-southeast winds will aid in providing moisture to the area. Expect variable weather conditions as local, orographic and diurnal effects generates afternoon convective activity, increasing the risk of flooding during the afternoon for sectors of interior and western Puerto Rico. Lines of convection (showers and thunderstorms) can also develop from the USVI, Vieques, Culebra, and from El Yunque. Periods of passing overnight and early morning showers are also forecast across windward sectors of the islands. With available moisture and east to east-southeast winds, heat indices in coastal, urban and lower elevation areas can reach above 108 degrees Fahrenheit. The Climate Prediction Center`s (CPC) Global Tropics Hazards Outlook indicates a greater than 50% probability of above-average rainfall across the northeastern Caribbean during the period. The National Hurricane Center (NHC) is monitoring an area, currently in the central tropical Atlantic, with a medium cyclonic formation chance through the next seven days. While it`s too early to assess any potential impact on our forecast area, please continue to remain vigilant and monitor future forecast updates from the NHC and from WFO San Juan. && .AVIATION... (18z) SHRA and TSRA are resulting in MVFR conditions across all TAF sites. Winds will continue from the E-SE at up to 15 knots with gusts. TSRA and SHRA may lead to lower ceilings across the mountains and reduced visibility. Another round of SHRA with TS is forecast for all eastern TAF sites from 09/09Z to 09/15Z. && .MARINE... A surface high pressure across the Atlantic will promote gentle to moderate easterly winds over the next few days. An upper-level trough to our north and a broad tropical wave moving in from the east will boost shower and thunderstorm activity during the next few days. Thunderstorms will affect the coastal waters of western Puerto Rico each afternoon. && .BEACH FORECAST... A moderate rip current risk is present along the northern and eastern-facing beaches of Puerto Rico and Culebra. Low risk elsewhere, however, life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 4 PM AST this afternoon for PRZ011. VI...None. AM...None. && $$ SHORT TERM...LIS/WS LONG TERM...MRR AVIATION...LIS/WS PUBLIC DESK...MMC/RVT
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