Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
947 FXCA62 TJSJ 150743 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 343 AM AST Wed Jul 15 2026 ...New LONG TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER... .KEY MESSAGES... Issued at 340 AM AST Wed Jul 15 2026 * Moderate concentrations of Saharan dust will continue to bring hazy skies across the region today, before gradually decreasing by Thursday early in the morning. * A limited heat risk is expected today due to warm daytime temperatures and limited moisture. Although in general heat indices are forecast to remain in less than 108 degrees, some localized areas can experience heat indices of 108 degrees for brief moments. * An increase in shower frequency and thunderstorm coverage is forecast for Thursday as moisture levels climb due to an approaching surface disturbance and upper-level instability. Dry conditions will return rapidly on Friday, quickly lowering rain chances and restoring a dry weather pattern across the islands. * A low risk of rip currents will remain in effect across the all coastal beaches of Puerto Rico and the U.S. Virgin Islands. && .SHORT TERM...(Today through Wednesday)... Issued at 340 AM AST Wed Jul 15 2026 A quiet night was observed across the island. Minimal cloud cover and no shower activity were detected by Doppler radar. In terms of temperatures, unofficial weather stations across the region reported overnight lows in the low to upper 60s across the mountains, mid to upper 70s along western coastal sectors, and between 80 and 82 degrees across the San Juan metropolitan area. Winds prevailed from the east at 5 to 10 mph. At the surface, the local weather pattern is primarily dominated by the interaction between an induced trough and a high pressure system centered over the mid-Atlantic. This interaction will maintain a steady easterly wind flow across the area. Under this pattern, a drier airmass will hold in place as seen by GOES derivative satellite imagery, which shows precipitable water (PWAT) values around 1.3 inches, along with an ongoing presence of Saharan dust particulates. Aloft, a cut-off low at the 250 mb level just north of the area, which continues to provide cooler temperatures in the mid-levels (500 mb) ranging between -6 and -7 C. Although these upper-level dynamics create somewhat favorable conditions for vertical development, a severe lack of mid-level moisture (700 to 500 mb) tracking near the dry 25th percentile will successfully inhibit any significant shower development. In terms of heat, two major factors will reduce the threat. First, the weather pattern will feature significantly less moisture across the region. Second, daytime maximum temperatures are forecast to remain one to two degrees below the 95th percentile. This combination will limit peak temperatures and heat indices, resulting in a mostly limited heat risk for the area today. Conditions are forecast to change slightly by Thursday as a brief surface disturbance moves across the region under the prevailing easterly wind flow. This setup will drive a localized surge in moisture at the 850 mb level, leading to an increase in overall shower probabilities across the forecast area. Initially, a minor increase in the frequency of passing morning showers is expected across the U.S. Virgin Islands and eastern Puerto Rico. As the day progresses, high-resolution modelsincluding the NMM and GFSsuggest the development of afternoon showers across the mountains and interior-western sections of Puerto Rico. While widespread significant rainfall is not anticipated, any localized showers that manage to develop over western Puerto Rico have the potential to produce up to an inch of rainfall if the forecast variables match at the perfect time. Another shift in the weather pattern is expected by Friday. While some moisture will linger, it will be in much smaller quantities. The surface high pressure will extend further westward into the Caribbean, tightening the pressure gradient over the local zone and causing an intensification of easterly winds. Of notable concern for Friday is the 925 mb temperature modeling, which shows a significant peak. This spike in low-level temperatures, combined with the returning breeze, will increase the potential for an elevated heat risk across the island to end the workweek. && .Long Term(Saturday through Wednesday)... Issued at 340 AM AST Wed Jul 15 2026 Typical summertime weather is expected through the weekend as weak upper-level ridging maintains warm and humid conditions with isolated showers in the afternoon over western PR, while the rest of the islands will remain dry each day. Beginning Sunday and continuing through Tuesday, a weak upper- level trough will gradually cool temperatures aloft and weaken the ridge, allowing atmospheric instability to increase. As a result, afternoon and evening thunderstorms are expected to increase from isolated to scattered at times, with Monday and especially Tuesday offering the greatest coverage of rainfall. While widespread severe weather is not anticipated, locally heavy downpours may result in brief ponding of water on roadways, particularly in urban and poor drainage areas. Frequent showers and occasional lightning will remain the primary hazards. Each day, visitor and locals should experience warm conditions through the period as low-level temperatures remain above seasonal averages. Afternoon heat indices will likely exceed normal values, especially across urban and coastal locations. People are urged to stay hydrated, seek shade or air conditioning during the hottest part of the day, and limit prolonged outdoor exertion. && .AVIATION... (06Z TAFS) Issued at 340 AM AST Wed Jul 15 2026 VFR conditions are expected to continue across all TAF sites. Slight visibility reductions due to suspended haze (HZ) will persist for most of the period, with improvements expected for TIST & TISX after 15/23Z, and for TJSJ after 16/03Z. Localized afternoon SHRA over western/interior Puerto Rico may result in VCSH at TJBQ between 15/19Z and 15/21Z. While haze will remain present, ceilings are expected to remain VFR with only FEW clouds expected between 3,000 and 4,000 feet. && .MARINE... Issued at 340 AM AST Wed Jul 15 2026 A surface high over the central Atlantic interacting with the PanamaColombia Low will maintain a tight pressure gradient across the region, supporting moderate to fresh east to east-southeast winds and moderate to choppy seas through much of the week. Moderate to high concentrations of Saharan dust embedded within a drier air mass will continue to spread across the region throughout the day, resulting in hazy skies and locally reduced visibility. A trade wind perturbation is expected to move across the area on Thursday, increasing the potential for passing showers and isolated thunderstorms, particularly during the afternoon over western Puerto Rico. && .BEACH FORECAST... Issued at 340 AM AST Wed Jul 15 2026 A low risk of life-threatening rip currents is expected tomorrow. Although the risk is low, dangerous rip currents can still occur, especially near groins, jetties, reefs, and piers. Always swim near a lifeguard whenever possible and heed the advice of local beach patrols and beach warning flags. Beginning Thursday, an east to east-southeast wind flow will increase the rip current risk to moderate along portions of the north, east, and southeast-facing beaches of Puerto Rico, Vieques, Culebra, and St. Croix. The moderate risk is expected to expand to most local beaches by the weekend. Beachgoers should continue to swim near lifeguards whenever possible, heed beach warning flags, and never swim alone A limited to elevated extreme heat risk is also expected at many local beaches today through the first half of the week. Stay well hydrated, seek shade whenever possible, and apply sunscreen to help reduce the risk of heat-related illnesses. && .FIRE WEATHER... Issued at 340 AM AST Wed Jul 15 2026 An elevated fire danger risk is forecast across the regional islands today. Under the influence of a dominant dry air mass and Saharan dust, minimum relative humidity (RH) values are expected to drop into the low-to-mid 40s across the southern plains, and into the low 50s across portions of northern and eastern Puerto Rico during the peak heating hours of the day. At the same time, easterly winds will persist at 10 to 15 mph with stronger, gusty conditions expected. Given the combination of dry soils, low RH values, and breezy conditions, any fires that develop could spread rapidly. Consequently, a Fire Danger Statement (RFD) has been issued and will remain in effect today from 10:00 AM to 4:00 PM AST for the southern plains, as well as northern and eastern sectors of Puerto Rico. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM, KEY MESSAGES & AVIATION...LIS LONG TERM....MMC MARINE & BEACH FORECAST...CAM