Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
736 FXCA62 TJSJ 252042 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 442 PM AST Sat May 25 2024 .SYNOPSIS... We anticipate showers and thunderstorms to develop across portions of Puerto Rico, particularly the central, north, and west sections each afternoon. Although a ridge aloft is expected to build during the workweek, plenty of moisture will continue to prevail. As a result, any prolonged period of showers and thunderstorms will result in urban and small-stream flooding. The driest day in the short term, Sunday. The aforementioned available moisture and the prevailing east to east southeast winds will promote heat index values that can affect individuals sensitive to heat by tomorrow. && .SHORT TERM...Tonight through Monday... In the morning, cloudy skies and calm weather conditions prevailed across Puerto Rico and the U.S. Virgin Islands. By the afternoon, showers started to develop along the interior and western municipalities of Puerto Rico. Temperature-wise, they remained in the upper 80s to low 90s along the coastal and urban areas, while over the higher elevations, they stayed in the upper 70s to low 80s. The prevailing wind flow was out of the east-southeast throughout the day. Overnight, expect some showers to develop along the eastern half of Puerto Rico and Saint Thomas. Minimum temperatures should remain in the upper 70s to low 80s along the coast and in the 70s across the mountains. Wind-wise, the wind flow is expected to stay from the east-southeast. On Sunday, we foresee mostly stable, warm weather conditions along with some hazy skies, particularly in the morning hours. The deep-layered trough will continue to weaken while the mid- levelridge remains aloft. Moisture content will decrease slightly, remaining belownormal to near-normal levels. Despite this decrease inmoisture,subsidence aloft will exacerbate warmer temperatures across the islands, withheat index values reaching hazardous levels.With these conditions, it islikely that we meet HeatWarning criteria, particularly across northern coastal municipalities. Nonetheless, by the afternoon, we continue to forecast the typical short-lived afternoon convection over the northwestern quadrant. The latest model guidance continues to suggest an increase in instability from Sunday night into Monday as the leading edge of the tropical wave approaches the region. This will lead to numerous showers scattered over eastern Puerto Rico and the smaller islands by early Monday, as well as deep convective activity across the region, especially across western Puerto Rico in the afternoon. Consequently, there could be an elevated risk of flooding in the area once again. We encourage first responders, citizens, and visitors to continue to monitor the forecast for any updates. && .LONG TERM...Tuesday through Saturday... Although the ridge aloft will hold through the forecast cycle, plenty of moisture will continue to prevail without any erosion expected in the midterm. In fact, the latest guidance suggested precipitable water values exceeding 2.0 inches through at least midweek. Moisture may decrease somewhat by the end of the workweek into the weekend and remain trapped below 700 MB. At lower levels, easterly winds will prevail on Tuesday, becoming more southeast Wednesday and onwards as a surface high relocates across the central Atlantic. Under this evolving pattern, trade wind showers will continue to affect windward locations from time to time, with locally induced afternoon showers expected across western Puerto Rico each day. With GDI values greater than 25 expected much of the week, diurnal heating and sea breeze convergence, isolated to scattered thunderstorms, are expected each afternoon. Therefore, urban and small stream flooding is expected each afternoon, mainly across central and western areas of Puerto Rico and the San Juan Metro Area. In addition, available moisture and southeast winds will promote heat index values that can affect individuals sensitive to heat. At this time, the bulk of African Dust will remain south of the area for much of the week. Nevertheless, some may reach the area by midweek. && .AVIATION... (18Z TAFs) Mainly VFR conditions expected to prevail across all terminals. However, SHRA/TSRA over the interior and western PR may cause tempo MVFR conds at TJBQ, and mostly VCSH/VCTS at TJSJ/TJPS thru 22z. Low- level winds will continue ESE up to 11 kt. && .MARINE... An east to east southeast wind flow will continue to prevail across the local waters over the next few days. Weather conditions will improve on Sunday. Nonetheless, shower and thunderstorm activity is expected Sunday night into Monday with the next tropical wave passage. && .BEACH FORECAST... Seas will remain below 5 feet across much of the regional waters. Therefore, there is a low risk of rip currents across the local beaches of Puerto Rico and the U.S. Virgin Islands. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...MMC/ICP LONG TERM....OM AVIATION...DS PUBLIC DESK...LIS