Hilo

Tonight: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows 63 to 69 near the shore to 50 to 55 at 4000 feet. Light winds. Chance of rain 70 percent.

Sunday: Mostly sunny with isolated showers. Highs 75 to 81 near the shore to around 67 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy with isolated showers. Lows 62 to 68 near the shore to 48 to 54 at 4000 feet. Light winds. Chance of rain 20 percent.

Kona

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 71 near the shore to 45 to 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 50 percent.

Sunday Night: Partly cloudy with isolated showers. Lows around 70 near the shore to 44 to 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Partly cloudy with isolated showers. Lows 61 to 69 near the shore to 54 to 59 near 3000 feet. East winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

Sunday: Sunny. Isolated showers in the afternoon. Highs 74 to 81 near the shore to 70 to 77 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Lows 61 to 69 near the shore to 53 to 58 near 3000 feet. East winds up to 10 mph in the evening becoming light.

Kohala

Tonight: Partly cloudy with isolated showers. Lows 61 to 69 near the shore to 54 to 59 near 3000 feet. East winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

Sunday: Sunny. Isolated showers in the afternoon. Highs 74 to 81 near the shore to 70 to 77 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Lows 61 to 69 near the shore to 53 to 58 near 3000 feet. East winds up to 10 mph in the evening becoming light.

South Big Island

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 71 near the shore to around 50 near 5000 feet. East winds 10 to 20 mph shifting to the northeast after midnight. Chance of rain 50 percent.

Sunday: Mostly sunny with isolated showers. Highs around 83 near the shore to around 66 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy with isolated showers. Lows around 69 near the shore to around 49 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows 63 to 69 near the shore to 50 to 55 at 4000 feet. Light winds. Chance of rain 70 percent.

Sunday: Mostly sunny with isolated showers. Highs 75 to 81 near the shore to around 67 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy with isolated showers. Lows 62 to 68 near the shore to 48 to 54 at 4000 feet. Light winds. Chance of rain 20 percent.

Waikoloa

Tonight: Mostly clear. Isolated showers in the evening. Lows around 71 near the shore to 49 to 55 above 4000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the afternoon. Highs 81 to 86 near the shore to 66 to 73 above 4000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Lows around 71 near the shore to 49 to 54 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

The plume of moisture that is producing some beneficial rainfall this afternoon over the windward areas of the Big Island will shift towards Kauai late tonight into Sunday. A front approaching the state Sunday night into Monday, will bring added instability which should enhance rainfall intensity with the main band of moisture over Kauai Sunday night and moving towards Oahu on Monday. The frontal boundary is expected stall and dissipate near Oahu Monday night. Locally heavy showers will be possible Sunday night into Monday with some flooding impacts possible. Weather conditions should improve Monday night into Tuesday with trade winds returning across portions of the state on Tuesday.

Discussion

This afternoon's satellite and radar imagery shows scattered showers over the east and southeast Big Island. Rainfall totals have been relatively light with anywhere from 0.1 to 0.5 inches of rain in the past 6 hours. The scattered showers this afternoon should begin to taper off this evening over the Big Island, while this plume of moisture heads towards Kauai tonight. Showers should be on the increase late tonight over Kauai and linger through the much of the day on Sunday. Rainfall amounts should stay on the lighter side due to stable conditions aloft. Some scattered showers will also be possible on Oahu on Sunday especially during the afternoon.
As a front approaches the state Sunday night into Monday, instability will increase but overall the instability looks marginal at best with 500mb temperatures warmer than -10C throughout the event. But nonetheless with precipitable water values approaching 2 inches, showery weather is expected with embedded isolated thunderstorms possible Sunday night into Monday for the western half of the state. By Monday afternoon, the main band of moisture should be centered around Oahu. Some flooding impacts will be possible, but due to the marginal instability, extreme rainfall rates are not expected with this event. The front is expected to weaken Monday evening, but details regarding where the frontal boundary will stall still remains uncertain. Our latest forecast reflects the boundary stalling slightly more westward than our previous forecast with the main moisture boundary stalling around Oahu Monday evening. This forecast remains in good agreement with the latest 12Z ensemble guidance.
High pressure will build north to northeast of the state Tuesday into Wednesday, which should bring the return of our trade winds at least to our eastern half of the state on Tuesday. Some weak troughing north of Kauai may cause the winds to be lighter and out of the east-southeast direction for the western half of the state. Some lingering moisture will also produce scattered showers across the state through Wednesday. A drier pattern is expected for the second half of next week as an upper level ridge of high pressure builds over the state.

Aviation

Light to moderate ESE trade winds will continue through tonight as high pressure moves north of the islands. An area of increased clouds and showers is currently moving across the eastern half of the state this afternoon, bringing periodic MVFR conditions to windward slopes and coasts. A cold front will approach the state from the northwest tomorrow. Ahead of the front, winds will veer to become southerly across the western half of the state and bring widespread clouds and showers to Kauai.
Outside of the low clouds and showers moving into windward areas this afternoon/evening and the low clouds and showers that will move across Kauai and perhaps Oahu from the south tomorrow, VFR conditions will generally prevail.
AIRMET Sierra is in effect for mountain obscuration across windward and SE portions of Oahu, Molokai, Maui and the Big Island, with conditions lingering through the evening. AIRMET Sierra will likely be needed for Kauai tomorrow as showers increase across the western end of the state.

Marine

Moderate trades weaken and veer to SE from Oahu and points east and S in the vicinity of Kauai tonight as low pressure tracks well N of the area. The attendant cold front enters the western waters Sunday night where there will be a slight chance for thunderstorms. Moderate winds retain a SE component through mid- week.
The current large, medium period NW swell is tracking close to model guidance and has declined sharply since its early morning peak at the Hanalei and Waimea buoys. Surf has fallen below the advisory threshold for all shorelines and High Surf Advisories (HSA) have been allowed to expire. Small surf expected Sunday as this swell steadily diminishes. Deep low pressure presently situated just southeast of Russia's Kamchatka Peninsula will deliver a large, long period swell WNW (310) swell early next week with long period forerunners arriving by Sunday night. The distant source region of this swell compared to the present swell will focus energy in the longer period bands increasing confidence that surf will rise to well within the HSA range during Monday and perhaps approach warning criteria for N and W facing shores as it peaks Monday night through Tuesday. The swell then gradually subsides during the second half of the week.
Moderate SE flow maintains small chop along E facing shores while background energy out of the southerly quadrant maintains small surf for S facing shores.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov