Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
271 FXCA62 TJSJ 242051 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 451 PM AST Fri May 24 2024 .SYNOPSIS... Isolated to scattered showers are expected overnight across the eastern portions of Puerto Rico and the U.S. Virgin Islands. A wet and unstable weather pattern is expected to prevail through next week as a tropical waves approaches the local area from the southeast on Monday. Warm and hot temperatures will persist, with heat indices reaching the upper 100s mainly across the urban and coastal portions of the islands. && .SHORT TERM...Tonight through Sunday... Fair weather conditions prevailed during the morning hours under partly to mostly cloudy skies. Warm conditions were observed, once again, across the region due to southerly winds and the influence of a deep-layered trough over the Dominican Republic. The Luis Munoz Marin Int. Airport reported a maximum temperature of 91 degrees Fahrenheit. Across the local islands, daytime temperatures were observed in the upper 80s to low 90s mainly along the coastal and urban areas. Heat indices between 110-112 degrees Fahrenheit were observed across the north-central and southwestern portions of Puerto Rico. Late afternoon convection developed over portions of central and southwestern Puerto Rico. Showers and isolated thunderstorms affected mostly the San German area, where doppler radar estimated accumulations up to 3.0 inches of rain. This activity should gradually dissipate by the early evening hours. By Saturday into Sunday, a mid-level ridge will continue to move eastward as the deep- layered trough weakens. However, sufficient available moisture will enhance showers and isolated thunderstorms across the interior, northern and northwestern portions of Puerto Rico each afternoon. Slow-moving showers could enhance the risk of flooding in flood- prone areas. Therefore, the risk of flooding remains limited to elevated through the rest of the period. Despite the anticipated weather conditions, daytime temperatures will continue in the upper 80s to lower 80s across much of the area. Expect these conditions to prevail until early next week until the arrival of a tropical wave. Heat indices could reach the upper 100s, where a Heat Advisory may be issued in those areas during peak hours of the day before shower activity begins. Stay hydrated if engaging in outdoor activities. .LONG TERM...Monday through Friday... PREV DISCUSSION.../issued 544 AM AST Fri May 24 2024/ Model guidance indicates that a wet pattern will persist through the long-term forecast due to a moist airmass across the region as a tropical wave approaches from the east. As this tropical wave moves over the islands by late Monday, causing moisture content to rise above 2.0 inches, an increase of unstable weather is expected to last through the long term period. Weak ridging aloft throughout the week will help keep conditions somewhat decent, yet the continuation of the passage of weak short-wave troughs through Friday will maintain above-normal moisture and marginal instability. The National Blend of Models hints for heavier rainfall during the afternoon hours particularly across western/northwestern Puerto Rico under an east-southeast steering flow. The Galvez-Davison Index also suggests a similar scenario, with a high potential for observing isolated to scattered thunderstorms capable of producing heavy rainfall each day. With saturated soils and elevated streamflows from previous days of rainfall, the flooding risk will remain elevated. Therefore, we could expect urban and small stream flooding, as well as flash flooding and landslides in areas of steep terrain. Hot days are also to be expected with heat indices reaching in the 100s to 110s through the week due to the high RH values and heating from the summer sun, therefore heat advisories or warnings may be issued during this time. Saharan dust particulates are expected to arrive by early in the week. Expect hot and hazy conditions to prevail across sections with less rainfall. && .AVIATION... (18z TAFS) Mainly VFR conds will prevail across all terminals through the forecast period. Afternoon convection will develop along and north of the Cordillera Central affecting local terminals, especially JBQ/JSJ. SHRA/TSRA downwind from the USVI may create MVFR conds at IST/ISX thru this evening. Also, SHRA/TSRA en route from the Mona Passage and E-Caribbean could reach portions of USVI/ PR overnight. Surface winds will continue from the ESE at 5-15 kt but locally higher due to gusty winds and sea breeze variations. && .MARINE... Surface high pressure across the central and northeast Atlantic and an induced surface trough just northwest of the region will promote moderate southeast winds through late tonight. In addition, the proximity of a deep layer trough over the Dominican Republic and an easterly disturbance will aid in enhancing thunderstorm development across portions of the regional waters and local passages through at least this evening. Winds are forecast to diminish overnight and then become more easterly over the weekend. && .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...RAM LONG TERM....GRS AVIATION...CAM PUBLIC DESK...LIS