000 FXHW60 PHFO 281943 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 943 AM HST Sat Dec 28 2019 .SYNOPSIS... Low, overcast clouds will bring showers to mainly windward areas of Kauai and Oahu this morning. Strengthening northeast trade winds will push passing showers into windward areas of the rest of the state. Winds will turn from the east this afternoon, and then weaken over the western half of the state tonight. Winds will become gusty again Monday as high pressure strengthens to the north. Limited showers over mainly windward and mountain areas are expected into next week. && .DISCUSSION... Satellite shows showery low clouds over Kauai and Oahu this morning. The band is expected to sink southward today, focusing more on Oahu and Molokai by late this morning. Will be monitoring the band to ensure it dissipates as expected. Afternoon should be a more typical trade wind forecast with showers focused over the windward sides of the islands. Some minor tweaks were made to the Kauai forecast (winds, PoPs and associated fields) this morning, but the forecast philosophy remains the same. High pressure far north-northeast of the islands will move to the east slowly over the next few days as a cold front near the datelines movings to the east. Easterly winds today will shift to the east-southeast tonight and Sunday. Winds are expected to be stronger over/near the Big Island and Maui in this flow. Fewer showers are expected Sunday with a drier airmass moving in. The high pressure system will build back in from the east on Monday and Tuesday, allowing gusty trade winds to build back in state wide. This will bring trade wind showers focused over the windward and mountain slopes. The front mentioned above will be reinforced on Wednesday as an upper level trough approaches from the northwest. This will help push the surface front towards the islands, and the instability provided with the upper level trough will increase rainfall amounts. Winds are expected to veer from the southeast on Wednesday ahead of the front. Around this time, the global models begin to diverge in their handling of the weather pattern. The latest ECMWF run brings a more defined frontal system down the island through Friday, while the GFS has a weaker system. The ECMWF has northwesterly winds behind the front by Thursday. The GFS brings stronger winds that quickly turn to the northeast. The current forecast remains on the conservative side bringing scattered showers and cloudy skies over the western islands. We will continue to monitor future model runs to fine tune the forecast. && .AVIATION... Occasional MVFR conditions are occurring at PHLI and PHTO in low clouds and -shra. These conditions are expected to continue through the day and on into the evening hours. An east to west oriented band of showery low clouds will continue to impact north and east facing slopes of Kauai today. North through east sections of the other islands will be less impacted but there may still be some periods of MVFR over and near higher terrain. AIRMET Sierra is currently posted for mountain obscuration over Kauai, Oahu and the Big Island. Breezy to locally windy trade winds will cause some low level turbulence over and downwind of mountain ranges of Kauai and Oahu. Thus AIRMET Tango is posted for low level turb. && .MARINE... The ridge of high pressure north of the state will gradually slide southeast over the next several days as a front passes far north of the area. This will cause winds to slightly weaken and veer towards the southeast around Kauai, while locally strong easterly winds remain across the rest of the area. Currently, a Small Craft Advisory (SCA) remains in effect for waters around Kauai and the typical windy areas around Maui County and the Big Island. The SCA is expected to be dropped for waters around Kauai later today as wind speeds decrease. An upward trend in surf is expected through the rest of the weekend as a new moderate northwest swell slowly fills in late today into tonight and peaks Sunday below advisory levels. Additionally, a moderate short period north to northeast swell will add some texture to exposed north facing shores through tonight. A hurricane-force low developed east of Japan yesterday and tracked east during the past 24 hours. An ASCAT pass over night, showed a fetch of hurricane-force winds with the head of the fetch reaching about 1600 nautical miles from the state. This low is expected to track northeast today and gradually weaken. Although details will likely still be fine tuned, the latest forecast has the extra large northwest swell steadily filling in on Monday and likely peaking Monday night into Tuesday morning. This swell will likely result in warning level surf for north and west facing shores Monday into Tuesday and SCA in all exposed waters for seas. A small, long-period southwest swell is expected to arrive this weekend as well and could provide a small bump in surf along south facing shores. The locally strong trades will support choppy surf along east facing shores. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai Channel-Oahu Windward Waters. && $$ DISCUSSION...M Ballard AVIATION...Burke MARINE...Foster