Hilo

Tonight: Cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 59 to 67 near the shore to 48 to 54 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 80 percent.

Tuesday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 80 near the shore to 61 to 66 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Tuesday Night: Cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 58 to 65 near the shore to 46 to 53 at 4000 feet. North winds up to 10 mph. Chance of rain 80 percent.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 69 near the shore to 42 to 48 near 5000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 85 near the shore to around 65 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 69 near the shore to 41 to 48 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy with scattered showers. Lows 59 to 68 near the shore to 52 to 59 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 61 to 81. East winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 58 to 68 near the shore to 50 to 57 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy with scattered showers. Lows 59 to 68 near the shore to 52 to 59 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 61 to 81. East winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 58 to 68 near the shore to 50 to 57 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 71 near the shore to around 49 near 5000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tuesday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 82 near the shore to around 64 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy. Isolated showers in the evening. Lows around 69 near the shore to around 48 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 59 to 67 near the shore to 48 to 54 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 80 percent.

Tuesday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 80 near the shore to 61 to 66 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Tuesday Night: Cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 58 to 65 near the shore to 46 to 53 at 4000 feet. North winds up to 10 mph. Chance of rain 80 percent.

Waikoloa

Tonight: Partly cloudy. Isolated showers in the evening. Lows 67 to 73 near the shore to 45 to 51 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Sunny in the morning then becoming partly sunny. Breezy. Highs 80 to 87 near the shore to 63 to 69 above 4000 feet. Northeast winds up to 25 mph.

Tuesday Night: Partly cloudy. Isolated showers in the evening. Lows 66 to 72 near the shore to 45 to 50 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The potential for heavy showers and isolated thunderstorms over this Big Island is beginning to fade this afternoon as an upper level disturbance moves further away from the state. Across the rest of the state, a typical trade wind pattern will persist through the first half of the week, with showers favoring windward and mauka areas. Trades will weaken in the latter half of the week as another upper disturbance and a cold front approach, possibly leading to more widespread rain and thunderstorms.

Discussion

A broad and weakening upper level low can be seen east-southeast of the Big Island on water vapor imagery this afternoon. While the effects from its associated instability are waning this afternoon, precipitable water values near 1.7 inches as measured on Hilo's 00Z upper air sounding, cooler temperatures aloft and diurnal heating will maintain the potential for moderate to heavy showers across the Big Island through the afternoon and early evening. On the summits, the dusting of snow/ice that was seen on the webcams this morning melted by the afternoon, with no additional wintery precipitation expected in the short term forecast as the low aloft moves further away from the state. For the rest of the island chain, expect typical trade wind conditions, with clouds and showers favoring windward and mauka sections.
The upper level low will continue to lift northeast and begin to dissipate overnight. As it does so, mid level ridging will edge over the state from the west, increasing atmospheric stability. Moderate to locally breezy trade winds will persist through Wednesday as the surface ridge weakens and shifts southward, following a front passing to the north. This setup will result in a mainly stable and dry trade wind pattern, with the best chances for showers in windward and mauka areas during the night and early morning hours.
The next pattern shift is expected to occur on Thursday as a cold front approaches from the northwest, disrupting the trades. Beyond Thursday, forecast confidence decreases due to diverging model solutions, but there is general agreement on the front moving into the western end of the state sometime Thursday night into early Friday morning. Increasing moisture and instability associated with an upper level trough diving southeast across the state will increase the potential for showers and thunderstorms Thursday night through Friday as the front moves into the area. The upper level trough should then push east of the state this weekend with ridging building in its wake, bringing more stable conditions. Remnant moisture from the dissipating front may maintain rain chances through Saturday, but rainfall amounts should be minimal as the mid level ridge becomes more established. A semblance of northeast trades looks to return by Sunday as a weak front approaches from the northwest.

Aviation

AIRMET Sierra is posted for tempo mountain obscurations above 2500 feet over windward slopes of the Big Island. This AIRMET will likely be dropped sometime this evening as daytime cloud build ups decrease.
Elsewhere, trade winds will weaken slightly into Tuesday as a cold front passes north of Hawaii. Winds will focus clouds and showers over windward and mauka areas that will produce isolated mountain obscurations.

Marine

High pressure over the Northeast Pacific will gradually weaken and retreat northward. A weak cold front will dissipate over the northwestern offshore waters tomorrow. A second cold front will approach the state from the northwest on Thursday then weaken and stall over the central islands on Friday.
Light to moderate trade winds will gradually ease through Wednesday. Winds will become increasingly variable on Thursday in response to the second front. Trade winds should return over the weekend.
Meanwhile, an upper level disturbance southeast of the Big Island will continue to trigger isolated thunderstorms over the southern offshore waters. Conditions will persist through tonight and possibly tomorrow. Thunderstorms in the offshore and coastal waters are also a possibility on Friday in conjunction with the cold front.
A moderate long-period northwest swell is currently building in and should peak late tonight or Tuesday morning then decline through Thursday. A High Surf Advisory (HSA) remains in effect through Tuesday for north and west facing shores of Niihau, Kauai, Oahu, and Molokai and north facing shores of Maui. The swell is expected to peak late tonight or Tuesday morning before slowly declining through the week.
An even larger, long- period northwest swell that could potentially bring High Surf Warning (HSW) level conditions for most north and west facing shores is expected Friday night and Saturday from a strong West Pacific storm.
Surf along east facing shores will hold relatively steady through tonight then gradually decline through the end of the week. A small north swell could potentially elevate exposed shorelines Wednesday and Thursday. South shore surf will remain very small through the middle of the week. An out of season long-period south swell may move through the islands at the end of the week, bringing a sizable boost to south shore surf.

Fire weather

No critical fire conditions anticipated during the forecast period as low-level moisture remains sufficient and wind speeds remain below critical thresholds. In addition, a front could bring a period of more widespread rainfall to the islands around the end of the week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Tuesday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.

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Data Courtesy of NOAA.gov