Hilo

Tonight: Mostly cloudy. Occasional showers in the evening, then numerous showers after midnight. Lows 63 to 71 near the shore to around 56 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 90 percent.

Tuesday: Partly sunny with scattered showers. Highs 79 to 85 near the shore to 64 to 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 70 near the shore to 53 to 58 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 74 near the shore to 49 to 54 near 5000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 84 to 89 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows around 73 near the shore to 48 to 54 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 65 to 84. East winds 15 to 20 mph. Chance of rain 50 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 72 near the shore to 55 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 65 to 84. East winds 15 to 20 mph. Chance of rain 50 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 72 near the shore to 55 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 75 near the shore to around 53 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 86 near the shore to around 69 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy. Breezy. Lows around 74 near the shore to around 52 near 5000 feet. East winds 10 to 20 mph.

Puna

Tonight: Mostly cloudy. Occasional showers in the evening, then numerous showers after midnight. Lows 63 to 71 near the shore to around 56 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 90 percent.

Tuesday: Partly sunny with scattered showers. Highs 79 to 85 near the shore to 64 to 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 70 near the shore to 53 to 58 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 75 near the shore to 52 to 57 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Isolated showers in the afternoon. Highs 84 to 90 near the shore to 66 to 72 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tuesday Night: Mostly clear. Lows around 74 near the shore to 51 to 56 above 4000 feet. East winds up to 15 mph.

Detailed Forecast

Synopsis

A breezy and unstable trade wind flow will continue to produce periods of heavy showers and isolated thunderstorms through tonight, followed by decreased shower activity from east to west on Tuesday. Stable breezy trade winds will support a typical pattern of mainly windward showers late Tuesday and Wednesday. An increase in rainfall is expected late Wednesday into Friday.

Discussion

A mid- to upper-level low just southwest of the state will maintain somewhat wet conditions and a chance of heavy showers tonight. The weakening low aloft is not producing much forcing, but since precipitable water remains at an impressive 1.6 to 2 inches, widely scattered heavy showers and a few thunderstorms have been passing over and around the islands today, with many windward sites measuring 0.5 to 1.5 inches of rainfall. Since the low aloft will fill very slowly, expect continued passing showers, some heavy with a possible thunderstorm, tonight, and with soils nearly saturated from the past few days of rainfall, it will not take much to cause flooding issues over windward areas. Thus, we have opted to keep the Flood Watch in place. That said, there are hints of drier air aloft starting to move in from the east, and since snowfall has greatly diminished on the high summits of the Big Island, the Winter Weather Advisory has been cancelled.
Heavy shower activity will decrease over the island chain from east to west late tonight and Tuesday. The stubborn low aloft will gradually fill, allowing deep high pressure far north of Hawaii to bring in drier and increasingly stable conditions from the east. This could occur as early as tonight on the Big Island, with increased stability finally returning to Kauai tomorrow afternoon. The weakening low aloft will not be able to produce much forcing, and precipitable water will be decreasing. As a result, the flood threat will be diminished on Tuesday.
A breezy and stable trade wind flow will prevail statewide late Tuesday into Wednesday. Deep high pressure centered nearly 700 miles north of Hawaii will drive breezy trade winds and produce stable conditions with an inversion based around 8,000 ft. Expect a typical pattern of windward showers.
An increase in shower activity is due Wednesday night into Friday. The fuel for the increased rainfall will be a pocket of low- to mid-level moisture associated with the remnants of former Hurricane Kristy. The GFS and ECMWF are showing precipitable water well above 1.5 inches, which suggests a few heavy showers will be possible. The breezy trade winds will keep showers moving along, and a weak ridge aloft looks to maintain some stability. Thus, there does not appear to be a significant flood threat at this time.
Weaker trade winds are favored for the upcoming weekend as a north Pacific front erodes the high to our north. There are some differences between the latest GFS and ECMWF, with the GFS suggesting lighter and more east to southeast winds along with some instability.

Aviation

An upper level low will bring unsettled weather over the state through tonight with moderate to locally heavy showers favoring windward and mountain areas and some scattered showers over leeward areas as well. The threat for heavier showers should decrease over the eastern end of the state tonight as the upper level low drifts westward. Breezy to locally strong trades should persist through Tuesday.
AIRMET Sierra for mountain obscuration should persist through most of the evening and into tonight as another round of showers moves in this evening. Drier air should move in from the east late tonight, which could bring some improvement.
AIRMET Tango remains in effect for tempo moderate low-level turbulence downstream of island terrain below 8000 feet and is expected to continue through Tuesday.
AIRMET Zulu is in effect for the potential for moderate icing associated with the deep layered clouds across the state. The potential for icing will be greatest between 130 and FL220. The threat for moderate icing should decrease over the eastern half of the state by Tuesday.

Marine

High pressure far northeast of the islands will persist through the week, supporting moderate to locally strong trade winds. A Small Craft Advisory is currently in effect for the typically windier waters around Maui County and the Big Island. This SCA will likely need to be extended through much of the week as the locally strong trades persist. Instability associated with an upper low near the islands will continue the potential for locally heavy showers and/or isolated thunderstorms in portions of the coastal waters through Tuesday morning. However, a drier, more typical trade wind pattern will return to the region on Tuesday.
Surf along north-facing shores will gradually decline as a small, medium-period north swell wanes through Tuesday. Another small northwest swell is possible Thursday, with potential for a bigger long-period northwest swell next weekend.
Meanwhile, a small long-period south swell will slowly decline through tonight, but a small, medium- to long-period reinforcement will arrive on Tuesday and keep surf mostly steady along south-facing shores. South shore surf will then gradually decline through the rest of week. Additionally, surf will remain elevated along east facing shores over the next couple of days due to the combination of small long-period east swell generated by former major Hurricane Kristy and short-period wind waves from the locally strong trades.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov