A high pressure system will strengthen north Hawaiian Islands, producing moderate to locally windy trades. Light to moderate showers will focus over windward and mauka areas with brief showers spilling over to leeward areas, especially during the overnight and early morning hours. Winds will ease and possibly shift out of the southeast during the second half of the week and into the weekend as the high shifts northeast of the state and a weak frontal boundary approaches the state from the northwest.
Two radars are currently out of service, limiting radar coverage from Oahu to northern portions of the Big Island. Satellite imagery shows a band of low level clouds with embedded showers moving east to west across the state. Over the past 6 hours, rainfall totals ranged from 0.20 to just under 1.0 inches across windward areas, with some leeward areas seeing 0.10 to 0.75 inches.
The soundings this morning show inversion heights have increased to 10,000 ft to 11,000 ft at the Lihue and Hilo sites. These elevated inversion heights have allow windward showers to spill over to leeward areas of the smaller islands overnight.
Inversion heights will drop to near 4,000 ft for the western half of the state and near 7,500 for the eastern half of the state as drier air filters in during the day today. This will lower rainfall chances, focusing precipitation mainly along windward slopes.
Another band of low level clouds with embedded showers will increase chances of rain tonight into Monday. Combined with elevated inversion heights, brief showers will again spill over to leeward areas of the smaller islands.
The remainder of the short term forecast generally repeats this pattern of passing light showers focusing along windward and mauka areas during the day and slightly enhanced showers overnight with spillage to leeward areas driven by showers embedded in the trade wind flow and lingering instability aloft.
A surface high to our north will strengthen today, allowing winds to become breezy to locally windy at higher elevations and ridges. Gusty winds will also develop downslope of leeward areas this afternoon has inversion heights lower. These conditions will hold through the first half of the week with minor fluctuations.
The second half of the week and into the weekend the high is expected to shift northeast of the state as a weak front approaches from the northwest. This will result in surface level winds weakening and possibly allow for a hybrid trade wind and land/sea breeze pattern to develop. In addition, upper level instability from a trough swinging from the northwest to southeast over the state could make for enhanced showers during this time. However timing and position of the upper level trough and surface front start to diverge between the GFS and ECMWF deterministic guidance thus there remains low confidence in the extended forecast at this time.
Breezy trades will persist through the forecast period. Isolated to scattered showers will be concentrated mainly along windward and mauka locations early this morning, then again by tonight. Some of the shower may produce brief periods of MVFR ceilings and visibility.
AIRMET Sierra remains in effect for north through east sections of the Big Island below 2500 feet due to low clouds and showers. Sierra will likely be canceled later this morning as conditions improve.
AIRMET Tango remains in effect for for tempo moderate turbulence downwind of terrain below 9000 ft.
High pressure north of the islands maintains fresh to strong trades through at least mid week. A Small Craft Advisory (SCA) is in effect for all waters except windward Big Island as trades are forecast to strengthen today and tomorrow.
Declining NNW swells will keep small surf in place today before dropping off on Monday. Expect tiny levels along north facing shores through much of the week before a small northwest swell arrives towards the end of the week.
A mid to long period south-southwest swell will decline today and remain small through much of the week with background south swells. A small long period swell is possible next weekend.
Rough trade wind swell will produce above average surf for E shores through Tuesday before declining with weakening trades mid-week.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.
