SynopsisHigh pressure north of the state will maintain moderate trade winds through mid week. The trades will strengthen Thursday and remain strong through the weekend. Showers will favor windward and mountain areas with an increase in showers expected as the trade winds increase.
DiscussionHigh pressure far to the north is propelling island trade winds at moderate speeds with breezy conditions throughout the state. An old frontal band is bringing clouds and showers to windward areas from the Big Island to Oahu this afternoon with some showers reaching leeward locations. This band will sag to the south and west through the night before clearing the area by tomorrow morning. A similar frontal band will bring clouds and showers Wednesday and Wednesday night as it passes from northeast to southwest through the island chain.
The high pressure will maintain moderate trade winds through midweek with limited showers focusing over windward and mountain areas with passing leeward showers over the smaller islands. The leeward Big Island will continue to see a diurnal pattern of increasing afternoon clouds with scattered showers forming over the slopes.
Trade winds will ramp up for the second half of the week as the high pressure to the north strengthens and sinks south. Expect a jump in the windspeeds between Wednesday and Thursday with breezy conditions and strong gusts. Strong trades will continue through the weekend as the high remains in place.
Upper level ridging will keep a cap on showers through Friday afternoon with light to moderate rainfall amounts expected within trade showers. An upper level trough is expected to push the ridge to the south later on Friday and bring cooler temperatures aloft over the islands. The cooler temps will increase instability and allow for increased shower coverage and intensity Friday night and into the weekend. With the strong trades and increasing cloud growth, expect a wet trade wind regime over the weekend and into next week.
AviationWinds will ease slightly overnight into Tuesday. AIRMET TANGO for low level turbulence over and immediately south through west of the mountains will likely stay posted through the routine issuance time, then be cancelled after 0400Z. However, pockets of isolated turbulence will remain possible as a strong low level inversion will remain. The 00z soundings showed the low level inversion sloping from 8.0 at PHTO to 5.5 kft at PHLI.
Moisture from an old frontal band will continue to move through the islands from Oahu to the Big Island, with conditions starting to improve in the next few hours, mainly for Oahu through Maui. AIRMET SIERRA for mountain obscuration is posted along north and east slopes of Oahu, Molokai, Maui, and the Big Island. This will be tailored as conditions improve.
MarineThe small craft advisory remains for the windier locations between Molokai and the Big Island through Tuesday. High pressure will build north of the state once again later in the week and will result in a return of strong trades. Another period with near gales in the windier marine zones and advisory-level surf along east facing shores will become a possibility over the weekend.
Surf along east-facing shores will ease through Wednesday with values remaining below advisory levels. A new long-period northwest swell will fill in later tonight, peak late Tuesday through Tuesday night, then gradually ease later Wednesday through Friday. Surf heights will respond, but should remain well below advisory levels through the peak. A small subsiding south swell will remain into Tuesday translating to a slight bump in wave heights along south facing shores.
HFO Watches/Warnings/AdvisoriesSmall Craft Advisory until 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.