177 FXHW60 PHFO 311332 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 332 AM HST Tue Mar 31 2020 .SYNOPSIS... Moderate trade winds will decrease by Wednesday. Showers will increase today and Wednesday, mainly over windward areas, switching focus to interior and upslope areas in the afternoons by the end of the week. && .DISCUSSION... Moderate trades due to a high northeast of the main Hawaiian Islands will give way to lighter winds through the week. A front to the northwest of the islands will move to the east, disrupting trade wind flow by Wednesday. The surface ridge ahead of this front will likely be pushed across the islands by the end of the week. Through Wednesday, winds will be mostly out of the east, keeping showers focused over windward areas. An increase in low level moisture at this time will fuel additional shower activity. A weak upper trough approaching from the northwest will increase instability across the region, and a slight chance of thunderstorms exists tonight through Wednesday. Kauai received a lot of rain recently, and additional rain there could lead to minor flooding. A Flash Flood Watch may be needed for that island and this could be issued later today if conditions warrant. Winds will decrease for the second half of the week, which will allow development of land and sea breezes. Clouds and showers would then focus over interior and upslope areas during the afternoon hours. Another low and associated upper trough approaching from the northwest this weekend could bring another round of moisture to the islands, but it is too early to determine details. && .AVIATION... An upper low drifting in from the west will keep unsettled weather in the forecast for the next 24 hours with periods of showers and brief MVFR conditions. Lighter winds over the next few days will result in land and sea breezes developing along more sheltered west slopes of each island. An upper level jet stream will keep cirrus clouds over the state along with tempo moderate turbulence aloft. AIRMET SIERRA in effect for tempo mountain obscuration over north through east sections of Kauai and Oahu this morning. This AIRMET will decrease in coverage later this morning. AIRMET TANGO remains in effect for moderate turbulence aloft between FL250 and FL350 due to an upper level jet over the islands. This AIRMET will continue through the morning hours. && .MARINE... Moderate to fresh easterly trades associated with high pressure northeast of the state will trend down today through midweek. Light and variable winds will result Wednesday through the second half of the week as a broad trough and an upper disturbance move over the islands. This pattern will bring another round of heavy showers and a few thunderstorms over portions of the area by Wednesday. The trough will lift northward and away from the area as a cold front approaches and stalls to the west over the upcoming weekend. Prevailing background winds will become southeasterly by Thursday, then continue into the weekend. Surf along north and west facing shores will trend up today through Wednesday as a small, medium-period northwest swell builds down the island chain. Guidance shows low pressure forming south of the Aleutians, near the Date Line, tonight, then dropping southward Wednesday through Thursday to an area around 1000 nautical miles northwest of the state. North-northwest winds focused at the islands within the 320-340 directional bands will near, if not reach gale-force levels. Seas are forecast to climb into the 20-25 ft range within this area. Although most of this energy may end up missing the islands to the west, a moderate, medium-period north-northwest swell will remain a possibility Friday night through Saturday. A gradual downward trend is expected Sunday through Monday. Surf along south facing shores may trend up by Wednesday as a small, long-period south-southeast swell builds. Otherwise, background southerly swells should be enough to keep the surf from going flat later in the week through the upcoming weekend. Surf along east facing shores will remain up through midweek, despite the trades relaxing locally. Heights should trend down by the end of the week and upcoming weekend as the upstream fetch relaxes. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Powell AVIATION...Bohlin MARINE...Gibbs