FXCA62 TJSJ 192101 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 501 PM AST Sun May 19 2019 .SYNOPSIS...The combination of a developing surface low pressure across the western Atlantic and a surface high pressure across the east-central Atlantic will continue to promote a southeasterly flow through at least the middle of the week. A mid to upper- level trough located across the southwest Atlantic will continue to approach the local area from the northwest and be located north of the area by Thursday. Showers and thunderstorms are expected to develop across the northwest quadrant of Puerto Rico during the next several afternoons. More widespread activity is possible by the middle portion of the week as the mid to upper-level trough makes its closest approach to the local area. && .SHORT TERM...Tonight through Tuesday... Ridge aloft continues to gradually weaken as a mid to upper-level trough continues to gradually inch closer to the region. Meanwhile, at low-levels, a developing surface low pressure located east of the northern Bahamas will continue to move north- northeastward into the western Atlantic during the next couple of days. This will continue to induce a southeasterly flow as well as continue the moisture influx into the region. For tonight into Monday, latest model guidance is indicating a surge in low-level moisture with precipitable water values increasing to 1.9 to 2.0 inches. This is expected to produce scattered showers across portions of eastern Puerto Rico and the USVI tonight into the morning hours. Then, as this moisture combines with the daytime heating and local effects, moderate to heavy showers and isolated thunderstorms are expected to develop across the northwest quadrant of Puerto Rico during the afternoon hours once again. This could result in urban and small stream flooding, especially since it has rained across this general area during the last couple of afternoons and the soils are saturated. Similar pattern is expected for Tuesday as well as precipitable water values will continue to remain elevated, ranging between 1.7 and 1.9 inches. Therefore, isolated to scattered showers may affect portions of eastern Puerto Rico and the USVI during the morning hours followed by the development of more enhanced showers and thunderstorms across northwest Puerto Rico during the afternoon hours. Once again, some urban and small stream flooding cannot be ruled out with the afternoon activity. .LONG TERM...Wednesday through Sunday... .PREV DISCUSSION... /issued 515 AM AST Sun May 19 2019/ A mid to upper level trough is forecast to move from the western Atlantic and over the northeastern Caribbean between Wednesday and Thursday. This will provide upper level support for the development of showers and thunderstorms across PR and portions of the USVI. Precipitable water content is forecast to peak during this period between 1.75-2.00 inches, therefore the potential for flooding rains will be high. Another short wave trough is forecast to move just northeast of the region during the weekend. This will continue to provide divergence aloft to support afternoon convection. At lower levels, the absence of the trade wind cap and light southerly steering winds will allow for tropical moisture to pool over the region. Induced perturbations across the eastern Caribbean in combination with trough pattern aloft will increase the potential for shower activity with possible thunderstorms across the Caribbean waters and across the USVI/eastern sections of PR late in the weekend. && .AVIATION...VFR conds expected through the forecast period, except the possibility of TEMPO SHRA/TSRA across TJBQ and TJMZ until 19/22Z. Winds will continue from the ESE at around 10-15 KT with sea breeze variations and occasional gusts, decreasing to 10 KT or less after 23Z. SHRA activity tonight will cause VCSH across the USVI terminals and possibly TJSJ. && .MARINE...Marine conditions will continue to be in good shape with seas generally expected to range between 2 and 5 feet with winds up to 15 knots across the regional waters. A moderate risk of rip currents is expected across portions of the north and east-facing beaches of the islands through Monday. && .PRELIMINARY POINT TEMPS/POPS... SJU 78 89 77 89 / 40 40 30 40 STT 77 86 77 86 / 50 30 50 50 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...RAM LONG TERM....GL