Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
883 FXCA62 TJSJ 262104 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 504 PM AST Thu Sep 26 2024 .SYNOPSIS... The leading edge of a tropical wave will continue to increase moisture across the islands resulting in showers across the waters this afternoon. The axis of the tropical wave is expected to reach the islands late tonight and Friday, increasing the potential for showers and thunderstorms. Tomorrow, the flood threat will range from limited to elevated. Hazards include mudslides in steep terrain, urban and river flooding. && .SHORT TERM...Tonight through Saturday... The day began with tranquil conditions across most of the forecast area, with the exception of scattered showers and isolated thunderstorms affecting the U.S. Virgin Islands and local waters due to the leading edge of an approaching tropical wave. A gust of 39 mph was recorded in St. Thomas alongside the thunderstorm activity. Before cloud cover increased, heat indices increased, but did not persist for long, leading to the cancellation of the Heat Advisory for the remainder of the afternoon. The short-term forecast remains on track. By late tonight into Friday, moisture associated with a broad tropical wave will continue to impact the forecast area. The latest precipitable water (PWAT) models suggest values gradually increasing to above- normal levels, to around 2.3 inches tomorrow. This tropical wave will enhance the potential for rainfall and thunderstorm activity across the islands. The flood threat will range from limited to elevated. Hazards include mudslides in steep terrain, urban and river flooding, and in poorly drained areas. By Saturday, a broad ridge will develop over the western Atlantic, maintaining an easterly flow at the surface, while another upper-level low develops over the Leeward Islands. Precipitable water values will decrease to around normal values, limiting widespread rain activity; however, typical afternoon showers and isolated thunderstorms are expected to develop over the western sections of Puerto Rico due to a combination of daytime heating and local effects. Warm to hot conditions are expected to continue over the next few days, maintaining a limited to elevated heat risk, especially in areas that receive little rainfall. && .LONG TERM...Sunday through Wednesday... PREV DISCUSSION... /issued 455 AM AST Thu Sep 26 2024/ After the passage of a weak tropical wave across the islands on Saturday, a drier airmass is expected to quickly move into the area. Therefore, mainly calm and stable weather conditions are anticipated from Sunday onward. A migrating surface high pressure located over the Bahamas and moving into the central Atlantic will promote easterly winds until Tuesday. On Wednesday, this surface high is expected to be located north or over the local islands promoting winds from the northeast. Shower activity will be limited during this period. However, passing showers dragged by the trade winds cannot be ruled out across the eastern municipalities of Puerto Rico and the USVI. In the afternoon hours, some localized showers are possible due to the combination of moisture, warm temperatures and local effects. Hot temperatures are very likely during most of the long-term period with highs reaching the mid 90s along the coastal and urban areas. Precipitable water will be mostly between 1.55 to 1.80 inches from Sunday through at least late Tuesday. && .AVIATION... (18Z TAFS) TSRA/SHRA will impact the local flying area due to an approaching tropical wave. We could anticipate brief period of MVFR across the local terminals, especially IST/ISX/JSJ/JBQ. TSRA across western PR are expected to taper off around 26/23Z. But another round will affect the islands by early tomorrow morning. Periods of reduced VIS and low ceilings are possible in these areas. Winds will be mainly from the E at 10-15 kt with see breeze variations and higher gusts, becoming calm to light and variable btwn 26/23z-27/10z. && .MARINE... A weak high pressure ridging over the region will maintain gentle to moderate easterly winds over the next few days. A northerly swell will maintain seas to around 4 to 5 feet through the weekend. Showers and thunderstorm activity will continue and increase late tonight and Friday as a tropical wave move across our region. && .BEACH FORECAST... There is a moderate risk of rip currents along the northern side the islands and will continue through the weekend. Life-threatening rip currents are possible in the surf zone, exercise precaution. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...YZR/MNG/CVB LONG TERM...GRS AVIATION...CAM/CVB PUBLIC...ERG