Hilo

Tonight: Occasional showers and isolated thunderstorms. Lows 63 to 69 near the shore to 54 to 59 at 4000 feet. East winds up to 15 mph shifting to the west after midnight. Chance of rain near 100 percent.

Sunday: Cloudy with scattered showers and isolated thunderstorms. Highs 79 to 84 near the shore to around 66 at 4000 feet. South winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with showers. Lows 65 to 70 near the shore to 54 to 60 at 4000 feet. East winds up to 10 mph shifting to the south after midnight. Chance of rain 90 percent.

Kona

Tonight: Cloudy. Scattered showers and isolated thunderstorms in the evening, then isolated showers and thunderstorms after midnight. Lows around 73 near the shore to 49 to 55 near 5000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Sunday: Cloudy. Isolated showers and thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 83 to 88 near the shore to around 67 near 5000 feet. Southwest winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Sunday Night: Cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 74 near the shore to 48 to 55 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 30 percent.

Waimea

Tonight: Cloudy and breezy. Numerous showers and isolated thunderstorms in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 64 to 72 near the shore to 56 to 64 near 3000 feet. East winds up to 25 mph. Chance of rain 70 percent.

Sunday: Cloudy with scattered showers and isolated thunderstorms. Highs around 79 near the shore to 67 to 78 near 3000 feet. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Kohala

Tonight: Cloudy and breezy. Numerous showers and isolated thunderstorms in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 64 to 72 near the shore to 56 to 64 near 3000 feet. East winds up to 25 mph. Chance of rain 70 percent.

Sunday: Cloudy with scattered showers and isolated thunderstorms. Highs around 79 near the shore to 67 to 78 near 3000 feet. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

South Big Island

Tonight: Cloudy and windy. Scattered showers and isolated thunderstorms in the evening, then isolated showers and thunderstorms after midnight. Lows around 74 near the shore to around 53 near 5000 feet. Northeast winds 10 to 30 mph. Chance of rain 40 percent.

Sunday: Windy. Cloudy with isolated showers and thunderstorms. Highs around 85 near the shore to around 67 near 5000 feet. East winds 10 to 30 mph decreasing to 10 to 20 mph in the afternoon. Chance of rain 20 percent.

Sunday Night: Mostly cloudy. Breezy. 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 20 percent.

Puna

Tonight: Occasional showers and isolated thunderstorms. Lows 63 to 69 near the shore to 54 to 59 at 4000 feet. East winds up to 15 mph shifting to the west after midnight. Chance of rain near 100 percent.

Sunday: Cloudy with scattered showers and isolated thunderstorms. Highs 79 to 84 near the shore to around 66 at 4000 feet. South winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with showers. Lows 65 to 70 near the shore to 54 to 60 at 4000 feet. East winds up to 10 mph shifting to the south after midnight. Chance of rain 90 percent.

Waikoloa

Tonight: Breezy. Cloudy with scattered showers and isolated thunderstorms. Lows around 74 near the shore to 53 to 58 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Sunday: Cloudy. Isolated showers and thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 84 to 89 near the shore to around 67 above 4000 feet. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 75 near the shore to 52 to 57 above 4000 feet. Northeast winds up to 10 mph shifting to the southeast after midnight. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Periods of heavy rainfall will continue this evening and persist into tomorrow, with isolated thunderstorms possible across the entire state. A Flood Watch remains in effect for all islands through Sunday afternoon. Drier, more typical breezy trade wind conditions are expected beginning on Monday through much of next week.

Discussion

This afternoon, deep moisture continues move over the islands, which has prompted moderate to occasionally very heavy rain throughout the day. The heaviest rain fell this morning over central and eastern Oahu, as well as eastern Maui. However, during the afternoon, nuisance flooding has continued to be a concern across all major Hawaiian Islands. Latest satellite and radar trends show that recent rainfall rates have been trending down across the smaller islands, though the opposite is true for the Big Island where rainfall has become more widespread. There remains plenty of moisture, instability, and large scale lift over the state, and a Flood Watch remains in effect until 6 PM HST on Sunday for all Hawaiian Islands.
For tonight, hi-res guidance, as well as the GFS, are hinting at the possibility of a surge of trade winds moving across the islands from north to south. Meanwhile, ample moisture will remain in place, and will be further enhanced as an upper level trough deepens into a low and moves closer to the state. Atmospheric instability will increase as this upper level feature moves closer, and will maintain the possibility for deeper convection and isolated thunderstorms. With all of these ingredients in play, any slow-moving heavy showers or thunderstorms will continue to produce flooding concerns. Isolated thunderstorms have also been added statewide for tonight through Sunday based on the latest guidance.
On Sunday, trades will become locally breezy as the front north of the islands dissipates and ridging begins to build. The upper level low will move more directly overhead, providing increasingly unstable conditions aloft. With plenty of low to mid-level moisture still streaming across the state, it won't take much to kick off moderate to locally heavy showers over already saturated ground. With the strengthening trades, showers will likely transition to focus mainly over windward areas. However, showers will also still form in the more sheltered leeward areas, particularly over the Kona slopes of the Big Island where locally heavy rain has been added to the forecast again for Sunday afternoon.
As the upper low pushes west of the area and surface ridging builds to the north, a breezy and increasingly stable trade wind flow is expected for much of next week, beginning on Monday. Pockets of moisture riding in on the trades will provide occasional brief upticks in windward showers throughout the week.

Aviation

Trade winds will become breezy tonight spreading from the north end of the state to the south. An upper low will remain in the vicinity of the islands into early next week resulting in widespread, enhanced showers that will lower ceilings and visibility, and cause mountain obscurations. Trade winds will focus the worst of these conditions over windward slopes, but leeward areas will also be impacted at times. Isolated thunderstorms are possible through at least Sunday.
AIRMET Sierra is posted for mountain obscurations above 2000 feet MSL for windward sides of all islands, and above 3000 feet for leeward sides of all islands. This AIRMET will likely continue through tonight and Sunday morning for these areas. AIRMET Tango is posted for moderate turbulence at the high levels (FL200-400) due to an approaching jet stream.

Marine

High pressure will build far NE of the islands the next couple of days as a front that lies between the islands and the high gradually dissipates. Trade wind speeds are expected to increase tonight and Sunday, and remain fresh to locally strong for the next several days, primarily in response to the strengthening high, necessitating a Small Craft Advisory (SCA) for the waters around Maui County and the Big Island. In the short term, a preponderance of high-resolution regional and global model guidance indicates a brief period of enhanced trade winds overnight, and a SCA is in effect for all waters through early Sunday. A developing disturbance aloft will bring the potential for heavy showers and thunderstorms into Sunday.
The latest pulse of medium-period NE swell is dropping at near shore buoys, but not as rapidly as earlier in the day. Surf along E facing shores has dropped below High Surf Advisory (HSA) heights, and surf will remain below HSA levels for at least the next several days. However, the combination of strengthening trades and a small long-period E swell from Tropical Cyclone Kristy should produce elevated surf along E facing shores for most of the new week. A small to moderate medium-period N swell should arrive Sunday and peak on Monday, then gradually decline. A new long- period S swell is expected to slowly decline the next couple of days. A long period NW swell may arrive by Friday.

HFO Watches/Warnings/Advisories

Flood Watch through Sunday afternoon for all Hawaiian Islands.
Small Craft Advisory until 6 AM HST Sunday 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, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov