Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
483 FXCA62 TJSJ 312045 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 445 PM AST Fri May 31 2024 .SYNOPSIS... Short-term concerns include continued heat through the weekend, daily afternoon showers and thunderstorms mainly across the interior and western Puerto Rico, and the arrival of Saharan dust, contributing to hazy skies and elevated to moderate heat risk. Wet and unstable conditions are expected early next week due to an approaching tropical wave. && .SHORT TERM...Tonight through Sunday... Generally calm conditions prevailed during the morning hours with only a few spotty showers in the Caribbean Sea and eastern sectors of Puerto Rico. As it was expected, thunderstorm activity developed by the early afternoon hours across the northwestern quadrant of Puerto Rico leaving around 1 to 1.5 inches of rain. Weather conditions are expected to improve after sunset due to diminishing surface heating. A Flood Advisory was issued for Aguadilla, Isabela, and Quebradillas due to that rain activity. Temperature-wise, it was another hot day as southerly winds persisted, and a new record daily maximum temperature was set in San Juan Airport with 94F, breaking the old record of 93F of 2006. Under an east-southeast steering wind flow, a similar pattern is expected over the weekend with passing showers moving in over windward coastal areas of Puerto Rico and Caribbean Waters during the late night and morning hours, with convective activity clustering over the northwestern quadrant of Puerto Rico each afternoon and precipitable water values running around 1.70 to 2.00 inches. Any heavy rain could lead to some urban and small stream flooding. Due to an approaching tropical wave; now located at 50W, the moisture content will increase within the 75th and 90th percentiles from late Saturday onwards, higher than the climatological norm. For the remainder of the weekend, the GEOS-5 model continues to suggest Saharan dust particles suspended over the islands leading to hazy skies across the northeastern Caribbean and could slightly suppress rain development in some areas. The 925 mb temperatures will remain well above normal for this time of year through the weekend. High temperatures combined with above-normal moisture could promote hazardous heat conditions, particularly across coastal and urban areas. Therefore, it is very likely that Heat Advisories and possibly Excessive Heat Warnings may continue to be needed each day over the weekend. Residents and visitors are encouraged to limit outdoor activities, drink plenty of water, and wear lightweight clothing. && .LONG TERM...Monday through Friday... .PREV DISCUSSION... /issued 501 AM AST Fri May 31 2024/ The lingering moisture from a departing tropical wave is set to continue promoting shower and thunderstorm activity across the region on Monday, with some thunderstorms potentially being strong over western PR. Following this, a wet weather pattern is expected to unfold across the northeastern Caribbean as a mid-to-upper- level trough moves from the northwestern to the north-central Caribbean, while a deep layered ridge builds and holds just east of the Leeward Islands. This will promote divergence aloft and south-to-southwesterly wind flow at lower levels. Furthermore, global models are indicating the development of an elongated area of low pressure to our north/northwest through the first part of the week. In response, moisture pooling is generally expected across the local area through most of the long-term period, with guidance suggesting 2.00-2.50 inches of precipitable water content, peaking by midweek. Therefore, the risk of flooding rains will significantly increase across all the islands. As the southerly winds and high humidity persist, we can expect warm to hot conditions across the islands, particularly across St. Croix and most coastal municipalities of PR, on Monday. Afterward, it will depend on how much cloud cover and rainfall materialize over the islands. A drying trend is expected by Friday as the broad surface ridge becomes the dominant weather feature. && AVIATION... (18z TAFs) Mainly VFR conds expected across all local terminals. SAL will continue to spread across the region today, causing hazy skies and reduced VIS at times. Aftn SHRA/TSRA may cause brief tempo MVFR conds at TJBQ through 31/22z and between 01/16-22Z at TJSJ/TJBQ. Winds will prevail from the ESE at 10-15 kts with higher gusts and sea breeze variations, becoming light to calm and variable between 31/22Z and 01/13Z. && .MARINE... A moderate east to southeast wind flow will prevail across the region through Saturday, becoming easterly briefly on Sunday, and with a dominant southerly component through midweek next week. Thunderstorms are expected to develop through the weekend between the late afternoon and evening hours across the western waters of Puerto Rico. A wetter pattern is anticipated by Sunday into early next week as the next tropical wave will approach the region with increasing winds and seas across the Caribbean waters. && .CLIMATE... A new record daily maximum was set on the last day of May, when the high reached 94F. In total, four daily maximum records were set this month, as well as 15 daily warmest minimum. This month ended as the warmest May on record for the San Juan Area climate site, with an average temperature of 84.4F. The previous record was 84.1F set in 2020. & .BEACH FORECAST... A low risk of rip currents will continue tonight across most beaches of Puerto Rico, St. Thomas, and St. John while a moderate risk is expected across southwestern Puerto Rico, Vieques, and St. Croix. The risk of rip currents is expected to remain between low and moderate throughout the upcoming weekend. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-005-008- 010-011. VI...Heat Advisory until 5 PM AST this afternoon for VIZ002. AM...None. && $$ SHORT TERM/MARINE/BEACH FORECAST...YZR/RAM LONG TERM....DSR PUBLIC...RC AVIATION...ICP/RAM CLIMATE...ERG