Hurricane Season runs from June 1-November 30
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521 FXCA62 TJSJ 090844 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 444 AM AST Mon Dec 9 2024 .SYNOPSIS... Moderate east northeast winds will prevail today into Tuesday then increasing while becoming more north northeast by Wednesday and the rest of the workweek, as an induced surface trough develops east and northeast of the area and surface high pressure builds north of the region. Breezy conditions and pleasant temperatures and a mix of sunshine and clouds will persist with an even drier trend by the middle of the week. Choppy seas due to moderate to locally fresh winds are forecast across the Atlantic and Caribbean waters through most of the week with a small north to northwesterly swell forecast to spread across the offshore Atlantic waters today through Tuesday. && .SHORT TERM...Today through Wednesday... Earlier in the night, as the axis of the surface trough was positioned over the Mona Passage, Doppler radar detected strong showers along the northern coastal waters of Puerto Rico and parts of the Caribbean waters. Some of these showers moved across southeastern Puerto Rico, with radar-estimated rainfall reaching up to 0.70 inches in coastal areas of Maunabo. Currently, the trough axis has continued moving westward and is now over eastern Hispaniola, with shower activity diminishing for the most part. However, some showers persist over the regional waters and are expected to move across eastern portions of Puerto Rico and the smaller islands through the morning hours. Minimum temperatures once again ranged from the mid to upper 70s across coastal areas of Puerto Rico and the USVI, and from the mid to upper 60s across higher elevations and valleys of Puerto Rico. The synoptic pattern for the remainder of the short-term forecast period remains unchanged. Current GOES-16 infrared satellite data indicates that the most active portion of the polar trough, associated with the area of greatest divergence at upper levels, is well northeast of the forecast area. Model guidance suggests that, although a strong 250 mb jet will develop near the region, the forecast area will remain under its subsidence side, with the greatest divergence and diffluence pattern confined to areas farther northeast as the TUTT deepens. This setup will limit widespread convective activity across the region. Consequently, rainfall coverage expected for the next few days has been slightly reduced. However, surface-induced perturbations east of the Leeward Islands, associated with the upper-level pattern, will occasionally stream across the area. This will maintain moisture levels between the 50th and 75th percentiles, which are near climatological normals for most of the short-term period, with slightly lower values expected by late Tuesday night. Under a northeasterly steering wind flow, showery weather will affect windward sections of the islands during the night and morning hours. Additionally, certain low- to mid-level parameters will support convection if sufficient lifting occurs. These include cold air advection at mid-levels, which contributes to lower 1000-500 mb thicknesses and steeper lapse rates between the 700-500 mb levels. As a result, the combination of sufficient low-level moisture, sea breeze convergence, and marginal instability could lead to orographically driven convection each afternoon, particularly today. Expect a limited to localized elevated flooding risk each afternoon, mainly across interior and southwestern sections of Puerto Rico. .LONG TERM...Thursday through Monday... Latest model guidance remains persistent and continued to suggest the amplified TUTT will linger just east of the northern Leeward Islands while deepening through Friday along with a broad induced surface trough which will slowly shift westwards across the area by the weekend. This trough and possibly a weak surface low is forecast to eventually lift northwards while spreading across the northeast Caribbean and local region, as the TUTT lifts northwards into the Central Atlantic. Models continue to suggest that the proximity of this deepening and developing trough will aid in increasing instability in the upper levels, resulting in more favorable conditions for enhanced localized convective activity across the area by the end of the period. Precipitable water values are still expected to diminish and range between 1.60 to 0.95 through early Friday. Thereafter and into the weekend moisture content rebounds and values increase once again to near of slightly above normal 1.60 to 1.90 inches, as the broad surface trough spreads across the region from the east. During the early part of the period, moisture erosion and stable condition aloft are expected as all guidance suggest we should remain on the subsident side of the aforementioned upper trough. This in turn should help to limit widespread convective activity across the region. However by the weekend the pattern changes as the trough spreads across the area, moisture will increase once again and thus support much better potential for early morning and afternoon convection. Widespread convection and significant weather impacts are still not anticipated at this time but some localized flooding will be possible, with the wettest period so far being Saturday through Sunday due to the instability aloft and increasing moisture content. Mostly showery and an advective weather pattern can be expected at times but mainly across the windward coastal areas during the overnight night and early morning hours steered by moderate northeasterly winds. This will be followed by limited convective activity in the afternoons, primarily over the interior and southwestern portions of Puerto Rico through at least Friday. Thursday through Friday are forecast to be the driest days of the period. As mentioned, a shift in this weather pattern remains possible by the weekend and through the early part of the following week, as low level moisture and instability increases due to the developing of the surface-induced trough approaching the islands from the northeast and a polar trough sweeping across the west Atlantic. This will result in the best potential for showers and isolated thunderstorm development across the islands and coastal waters during the latter part of the period. Seasonal northerly wind pattern will also bring very pleasant temperatures across the area through the early part of the period, with winds forecast to becoming more easterly by the end as now suggested by model guidance. Occasional breezy conditions with an occasional advective pattern of passing overnight and early morning shower will be likely at times along the north and east coastal areas but widespread and impactful rainfall accumulations are not still not anticipated at this time. && .AVIATION... (06Z TAFS) Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, brief mtn top obscr ovr E PR til 09/12Z. Also, SHRA with possible iso TSRA may develop in and around TJPS btw 18z-22z. Sct mdt ocnly strong SHRA may move across the FA with some reaching the windward side of the islands aft 09/22z. SFC wnd light and variable to calm bcmg ENE 10-16 kts with some sea breeze influences and ocnl hir gusts aft 09/14Z. && .MARINE... A surface high pressure spreading across the southwestern Atlantic, will continue to promote a moderate east northeasterly wind flow across the regional waters. The pressure gradient will tighten across the area over the next few days promoting moderate to fresh winds. This pattern will result in choppy seas across the Atlantic and Caribbean waters. A small northerly to northwesterly swell will spread across the offshore Atlantic waters today through Tuesday. && .BEACH FORECAST... A small north to northwesterly swell will impact the northern and northwestern exposed beaches of the islands, potentially leading to hazardous beach conditions in localized areas today through Tuesday. However, the risk of rip currents will remain moderate for most coastal areas of the islands. Increasing trade winds will maintain choppy seas and hazardous beach conditions especially along the north and east facing beaches by Wednesday. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...CVB LONG TERM....RAM AVIATION...CVB
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