A broad high pressure ridge north of the islands will produce moderate trade winds through Monday. Wind speeds will weaken from Tuesday through Thursday as a weak surface trough moves into the island chain. Trade winds slowly return by the end of next week, reaching moderate wind speeds by next Sunday, as the stalled front north of the islands diminishes and a broad ridge builds back into the region.
Clouds and showers were once again focused on windward and mauka areas this afternoon. Trade winds were averaging 10 to 20 mph, with gusts near 30 mph in the typical breezy areas. These showers are forecast to continue into the night, and winds are forecast to slowly decrease after sunset.
Weak northwest flow aloft will become westerly Monday night as a large upper level low well to our north moves east across the Pacific. A weak surface trough will move toward the state, resulting in trades becoming southeast winds Monday night into Tuesday. The trough will enter the west end of the state Tuesday night, and winds behind the front will become light northerly or northwesterly. There is low confidence at this time on how far the trough will get, and the latest guidance indicates it will stall around Maui Wednesday night. East to southeast winds will develop Thursday night through Sunday as the trough recedes to the west. Looking very long range, a stronger trough/cold front may approach the state late next weekend.
Moisture will remain rather limited through the next week, with PW values near to or a little over an inch for most of the period. There are some indications that moisture may increase Thursday into next weekend, but confidence is low. In general, we will maintain trade-wind showers Monday and Tuesday, then switch to a land-breeze / sea-breeze pattern Wednesday and Thursday. This means showers will be mainly windward and mauka early in the week, transitioning to afternoon inland showers and mostly dry nights Wednesday and Thursday. As trades return late in the week, showers will become mainly windward and mauka again.
Moderate to breezy easterly trades will persist through tonight with clouds and brief showers favoring windward sites. Expect periods of MVFR ceilings and visibility in showers, otherwise widespread VFR is expected. Trade wind flow should weaken slightly during the day on Monday, with the weakening trend set to continue through mid-week.
There are currently no AIRMETs in effect, though AIRMET SIERRA may need to be added to north through east portions of select islands tonight as shower activity increases.
Fresh to locally strong trade winds will through much of the night as a stalled front weakens about 225 nm northwest of Kauai and surface high pressure farther to the northwest moves eastward. A Small Craft Advisory has been issued around Big Island and Maui County for tonight due to an expected short-lived increase in the trades. The surface high will steadily erode on Monday, leading to a steady decline in the trades. Another front passing north of the islands Tuesday and Wednesday will disrupt the trade winds. Gentle to moderate trade winds are expected to redevelop Thursday and Friday.
The current small northwest swell will decline tonight. A moderate northwest swell will build on Monday and produce surf above seasonal average during the peak Monday night and early Tuesday. This swell will slowly decline late Tuesday and Wednesday. A larger northwest swell could produce surf near the High Surf Advisory level Thursday, then lower Friday into next weekend.
A south-southwest swell will produce surf around seasonal average into tonight and will gradually decrease Monday and Tuesday, with mainly small background surf along south facing shores through the rest of the week.
Trade wind swell will slowly lower below seasonal average on Monday and will remain small through the remainder of the week.
Small Craft Advisory until 6 AM HST Monday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.
