446 FXHW60 PHFO 091936 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 936 AM HST Tue Oct 9 2018 .SYNOPSIS... A moderate trade wind flow will continue into midweek due to high pressure to the northeast of the state. Expect showers to favor the typical windward and mountain locations during this time. Winds will weaken during the second half of the week as the high begins to weaken and lift northward. A cold front approaching from the northwest will bring showers to more areas for the end of the week and into the weekend. && .DISCUSSION... A 1031 mb high was analyzed near 41N144W overnight, more than 1500 miles north-northeast of Honolulu. There is good model agreement with the high remaining nearly stationary for the next day or two, and then slowing weakening during the second half of the week as it begins to drift to the northeast. Have made some adjustments to the PoPs for today primarily over Maui County and the Big Island given that radar and satellite show clearer skies overhead to start the day. Still anticipating the windward locations to see more clouds and showers this afternoon. Trade winds will stick around for another day, but as the high begins to weaken and move to the northeast, our winds will once again weaken and turn to the southeast. A low far northwest of the islands is moving to the northeast bringing a surface trough towards the region. The models are in good agreement with a new surface low developing along this trough on Thursday, which will help to further disrupt our winds, leading to a lighter wind flow over the islands. This will likely lead to localized land and sea breezes, which will mean more clouds and showers over the interior of the islands during the afternoon. The global models have come into better agreement over the last 24 hours with the handling of this low. Heading into the weekend, this low will drop southward and bring a front closer to the islands. A shortwave ahead of the front looks to start moving down the island chain as early as Friday night, with the rain band associated with the front moving over Kauai Saturday night or early Sunday. The front then stalls over the central islands Sunday night and weakens Monday, with trades possibly making a re-appearance Tuesday into Wednesday. Dewpoints which were in the mid 70s recently making it feel muggy with the light winds last week have dropped to the upper 60s and low 70s. The front this weekend will usher in drier dewpoints to start the week. The latest runs of the GFS and ECMWF show dewpoints dropping into the low 60s on Monday. && .AVIATION... High pressure centered far NE of the islands will maintain moderate to locally strong trade winds through at least tonight. Although the trades are strengthening, the air mass is still unstable enough to negate the development of low-level turbulence over and downwind of the mountains. However, if a low-level inversion does form, AIRMET Tango may be needed later today. A broken band of clouds and showers embedded in the trade wind flow is currently gradually exiting the islands, with Kauai being the last to clear later this morning. Therefore, all AIRMETs for mountain obscuration have been dropped. The air mass across the island chain will be somewhat more stable and drier than yesterday, so expect less showers overall today and tonight. However, forecast models are hinting at another band of showers to affect the islands sometime Wednesday morning. No other AIRMETs expected through tonight. && .MARINE... Fresh to locally strong trade winds will decrease on Wednesday and Thursday. A 1031 mb surface high sitting far northeast of the islands will gradually weaken on Wednesday and Thursday, leading to the decline in the trades. A Small Craft Advisory (SCA) remains posted for the typically windy waters around the Big Island and Maui and will likely be dropped by Wednesday morning. A developing trough near or over the islands will disrupt the trades on Friday, followed by a weak frontal passage that will usher in gentle to moderate northerly winds during the weekend. SCA strength winds are not expected to redevelop through the middle of next week. East swell from distant Hurricane Sergio continues to slowly rise. PacIOOS buoys off of the Big Island, Maui and Oahu suggests swell heights of 4 to 5 feet at 13 seconds, large enough to produce High Surf Advisory (HSA) level surf across east facing shores of those islands. The HSA currently runs though tonight but will likely need to be extended through Wednesday night based on Wavewatch III output. The east swell is expected to gradually decline Thursday into the weekend. Surf near the October average is expected along north and south facing shores through much of the week. A northwest swell is expected to peak at 4 to 5 feet 12 seconds today, followed by a slightly smaller reinforcing swell on Thursday. A potentially larger north-northwest swell is due Sunday night and Monday. Small southwest swells will persist through much of the week, though a larger pulse tomorrow could produce south shore surf slightly higher than the October average. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Wednesday for Oahu Koolau- Olomana-Molokai Windward-Maui Windward West-Windward Haleakala- South Big Island-Big Island North and East. Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...M Ballard AVIATION...TS MARINE...Wroe