Hilo

Tonight: Partly cloudy with isolated showers. Lows 56 to 65 near the shore to 44 to 52 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 72 to 79 near the shore to 58 to 65 at 4000 feet. North winds up to 15 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 56 to 64 near the shore to 45 to 52 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy early in the evening then becoming mostly clear. Isolated showers early in the evening. Lows around 67 near the shore to 39 to 47 near 5000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 77 to 82 near the shore to around 62 near 5000 feet. Light winds. Chance of rain 20 percent.

Tuesday Night: Partly cloudy. Isolated showers in the evening. Lows around 67 near the shore to 40 to 46 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Partly cloudy with isolated showers. Lows 56 to 66 near the shore to 48 to 55 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 74 near the shore to 63 to 73 near 3000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 56 to 65 near the shore to 48 to 56 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Partly cloudy with isolated showers. Lows 56 to 66 near the shore to 48 to 55 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 74 near the shore to 63 to 73 near 3000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 56 to 65 near the shore to 48 to 56 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly cloudy early in the evening then becoming mostly clear. Isolated showers in the evening. Lows around 69 near the shore to around 47 near 5000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 79 near the shore to around 62 near 5000 feet. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 20 percent.

Tuesday Night: Mostly clear. Lows around 68 near the shore to around 47 near 5000 feet. East winds up to 10 mph in the evening becoming light.

Puna

Tonight: Partly cloudy with isolated showers. Lows 56 to 65 near the shore to 44 to 52 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 72 to 79 near the shore to 58 to 65 at 4000 feet. North winds up to 15 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 56 to 64 near the shore to 45 to 52 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly clear. Lows 64 to 69 near the shore to 42 to 48 above 4000 feet. East winds up to 15 mph.

Tuesday: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 77 to 84 near the shore to 61 to 66 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy. Breezy. Isolated showers in the evening. Lows 64 to 69 near the shore to 43 to 49 above 4000 feet. East winds up to 20 mph shifting to the southeast up to 10 mph after midnight. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A very stable north to northeasterly flow will bring an increase in light shower activity over portions of the island chain tonight through Wednesday as a shallow band of moisture moves down from the north. Weak trade winds will prevail Thursday, and a passing disturbance aloft may trigger spotty showers. Moderate trade winds and a typical pattern of windward rainfall is expected Friday through the weekend.

Discussion

Satellite and radar imagery show a band of moisture moving through Kauai, producing scattered light rainfall with rates generally under 0.25 inches per hour. This band of moisture is expected to continue to advance towards Oahu this evening, then on to Maui County overnight through Tuesday morning before really filling in over the Big Island Tuesday afternoon and lingering through Wednesday. Despite a shortwave aloft passing overhead, a mid level ridge should cap cloud depth below 10,000 ft and limit shower intensity. The reasonable worst case ensemble guidance is showing total rainfalls of less than 1 inch across terrain, which suggests modest rainfall. A stable north to northeasterly surface flow will focus rainfall along northeasterly slopes with a few light showers making it over to leeward areas. Dew points along the band will briefly rebound into the low to mid 60s, raising overnight low temperatures back around normal. Elsewhere of the band, clouds and chances of showers will be minimal and dew points will remain in the upper 50s, allowing overnight lows to drop slightly below February normal.
Weak trade winds will prevail on Thursday as a surface ridge to the north is eroded by an approaching front. The GFS and ECMWF have been showing that another front approaching from the northwest will stall before reaching the area. However, a passing shortwave aloft associated with the front may produce instability. Since sea breezes will likely overpower the weak trades, there is some chance that afternoon convection could produce spotty rainfall. The ECMWF has been keeping the moisture from this current band lingering around the state through Thursday that could fuel enhanced showers, while the GFS has been drying the area out and not picking up on a significant increase in moisture. Thus, there is some uncertainty on shower potential.
Easterly trade winds will build to moderate strength on Friday and Saturday as a surface ridge expands north of the state. A typical pattern of windward and mauka showers is expected through the weekend.

Aviation

An old frontal band will bring some light showers to the smaller islands during the next 24 hours, with some MVFR cigs/vsbys possible at times along north facing slopes and coasts. VFR conditions should prevail over the Big Island and leeward sections of the smaller isles.
AIRMET Sierra remains in effect for mountain obscuration on Kauai. The AIRMET may need to be expanded to include Oahu, Molokai and Maui later tonight.
AIRMET Tango may be needed for moderate upper level turb across Oahu and Kauai later tonight.

Marine

Moderate to locally fresh north-northeast winds are expected through tonight. As the high northwest of the state slowly tracks southeastward and drifts closer to the state, winds will gradually veer to the east and weaken Tuesday night through Thursday. The ridge of high pressure should be very close to the state by Thursday, which should allow for light to gentle winds. The ridge of high pressure should lift northward Friday through the weekend, which should bring the return of fresh to locally strong trade winds over the weekend.
The current moderate to large medium period north to north- northeast swell will remain moderate to large through tonight. Altimeter observations north of the islands showed a slight increase in wave height as slight reinforcement are expected to maintain High Surf Advisory (HSA) criteria through tonight and potentially extended through Tuesday depending on the potential buoy observations tonight. A Small Craft Advisory (SCA) is also in effect due to seas of 10 feet or greater for exposed waters and channels across the state. Lastly, a Marine Weather Statement (MWS) remains for Maui County windward waters and Big Island windward waters in regards to north facing harbors such as Kahului and Hilo through tonight because of the north- northeast swell. All of these products may need to be extended through Tuesday.
A new moderate long period west-northwest swell is expected to fill in later tonight and peak on Tuesday. A slightly larger long- period northwest swell is expected to fill in late Thursday and peak on Friday near advisory thresholds.
Surf along east facing shores should continue to see moderate surf throughout the week due to the long-lived north-northeast to northeast swells throughout the week. A reinforcing northeast swell is expected around Thursday, which could elevate surf along east facing shores near advisory thresholds. Surf along south facing shores will remain tiny through the forecast period with mainly background energy.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for Niihau, Oahu North Shore, Olomana, Maui Windward West, Kauai North, Kauai East, Koolau Windward, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Tuesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters.

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Data Courtesy of NOAA.gov