West Side

Today: Breezy. Partly sunny with isolated showers. Highs 74 to 80. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 64 to 70. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Saturday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 77. East winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

South Side

Today: Partly sunny. Isolated showers in the afternoon. Highs around 82. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows 62 to 72. North winds up to 10 mph.

Saturday: Partly sunny. Scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 81. Light winds. Chance of rain 50 percent.

North Shore

Today: Windy. Occasional showers in the morning, then numerous showers in the afternoon. Highs around 76 near the shore to around 59 near 5000 feet. East winds 10 to 30 mph decreasing to up to 30 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows around 67 near the shore to around 49 near 5000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 77 near the shore to around 61 near 5000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Central Maui

Today: Partly sunny. Breezy. Isolated showers in the morning. Highs 76 to 82. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 63 to 68. Northeast winds up to 20 mph. Chance of rain 20 percent.

Saturday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 79. Northeast winds around 10 mph in the morning becoming light. Chance of rain 50 percent.

Upcountry

Today: Breezy. Mostly cloudy with scattered showers. Highs around 56 at the visitor center to around 51 at the summit. East winds 10 to 20 mph shifting to the southeast up to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 44 at the visitor center to around 41 at the summit. East winds up to 15 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 57 at the visitor center to around 51 at the summit. Southeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 50 percent.

East Maui

Today: Windy. Occasional showers in the morning, then numerous showers in the afternoon. Highs around 76 near the shore to around 59 near 5000 feet. East winds 10 to 30 mph decreasing to up to 30 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows around 67 near the shore to around 49 near 5000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 77 near the shore to around 61 near 5000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Lanai City

Today: Partly sunny. Scattered showers in the afternoon. Highs 69 to 76. Northeast winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Lows around 62. Northeast winds up to 10 mph.

Saturday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 68 to 75. Light winds. Chance of rain 40 percent.

Kaunakakai

Today: Breezy. Partly sunny with scattered showers. Highs 64 to 82. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers in the evening, then mostly cloudy with isolated showers and thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows 54 to 69. East winds 10 to 15 mph. Chance of rain 40 percent.

Saturday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 65 to 82. East winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy trades will continue for one more day, but will ease by this evening. As a disturbance moves overhead today, expect increasing chances for heavy rain and isolated thunderstorms over the western end of the state, first for Kauai later today and then for islands farther east by Saturday. The wet weather will continue into early next week as a frontal boundary sinks back southward over the state. Strengthening trades will return a more typical windward and mauka-focused shower pattern, followed by more stable conditions by mid to late next week.

Discussion

Another breezy day is in store across the island chain today as a stationary front is located to the west of the state this morning with high pressure centered well to the north. It will not be as windy as previous days, however, and winds are expected to gradually decline by this evening. The front remains west of the offshore waters area at this time, and widespread cloud cover and a line of thunderstorms along this feature dominate the regional satellite imagery. Ahead of the front, thick high clouds have spread farther east over the island chain. Latest radar imagery shows a few showers embedded within the trades favoring windward and mauka sections of the islands early this morning. Upstream of the islands, an area of deeper moisture is forecast to move across the islands today, increasing windward and mauka showers, even as trade winds gradually ease and veer slightly.
An axis of deep moisture will approach from the west today as well as an upper-level trough swings overhead. The combination of increasing moisture and instability will bring the potential for localized flooding and isolated thunderstorms late this afternoon into Saturday, particularly across the western end of the state. Latest guidance continues to indicate cool temperatures aloft, with 500mb temperatures dipping down to near -13C. Although surface dewpoints may only reach into the mid-60s, continue to think there will be enough moisture, instability, and lift in the region to at least introduce a brief period of flooding potential across Kauai County, as well as some isolated thunderstorms. Additionally, the latest HREF guidance and CAMs do show the potential for heavy rain across Kauai during the evening, so the Flood Watch remains unchanged, and is in place for Niihau and Kauai from this afternoon through early Saturday morning. Hi-res guidance also suggests that there could be a brief window of heavy rain potential for Oahu as well early Saturday, but confidence is not high enough at this time to expand the watch.
Beyond the weekend, model guidance suggests that between Sunday night and Tuesday, moisture pooled along a horizontally-oriented frontal boundary will move back southward down the island chain as high pressure builds to the north between two nearby lows. This boundary will increase windward and mauka showers again as it moves through, followed by strengthening trade winds. By the second half of next week, mid-level ridging is expected to build overhead, supporting a more stable pattern with moderate to breezy trade winds.

Aviation

Trade winds will weaken this evening as high pressure in our area weakens and a low pressure system noses its way toward the islands. Isolated to scattered windward showers are expected during the day today, with more widespread activity moving in during the overnight period heading into Saturday. Conditions may drop to MVFR later tonight as these showers spread eastward to Kauai, leeward Oahu, and Molokai, potentially effecting the rest of Maui county by daybreak Saturday.
AIRMET Sierra is also in effect for mountain obscuration above 2 kft for north and east Big Island as shower activity increases across the area.
AIRMET Tango remains in effect for tempo moderate turbulence below 8000 feet over leeward sides of the islands as a result of continued breezy low level winds, as well as moderate turbulence aloft between 20kft and 38kft. Conditions are expected to improve as winds weaken through the period.

Marine

Strong trades will persist today, then begin to ease over the weekend as a gale nearby to the northwest lifts north- northwestward and away from the region. Winds may become light enough for a localized land and sea breeze regime to become established over the weekend. Seas will respond by gradually lowering, likely falling below the 10 ft Small Craft Advisory level by Saturday. In addition to the winds and seas, expect a wet pattern with isolated thunderstorms to develop by tonight as an upper disturbance moves over the state.
Surf along exposed east-facing shores will remain rough, with heights hovering around advisory levels today. A downward trend will follow over the weekend as winds diminish locally and upstream of the state.
Surf along exposed north- and east-facing shores will quickly build through the day Monday as a long-period north-northeast swell from a broad storm-force low evolves off the northwest Pacific coast this weekend. A large area of northerly gales between this system and a 1048 mb blocking high centered over the Aleutians will expand southward Friday through the weekend, with the head of the fetch reaching less than 1,000 nautical miles from the state. Heights will reach warning levels for exposed north- and east-facing shores by late Monday through Tuesday. Although a gradual downward trend is anticipated by midweek, additional pulses from this same system will keep surf above advisory levels for east-facing shores through much of the week. This swell direction will bring surf into some typically protected areas such as Kua Bay, West Maui, and exposed shores of Lanai.
Other impacts from this north-northeast swell direction could include significant erosion along some coasts and accretion at other locations as sand shifts opposite the typical swell direction, particularly along north-facing shores. Additionally, overwash along vulnerable sections of coastline and roadways will be possible beginning Monday night during high tide cycles. Mariners can also anticipate harbor surges in Kahului and Hilo.
Surf along exposed west-facing shores will rise early next week as a long-period northwest swell arrives from a broad storm-force low currently located over the far northwest Pacific near the Kurils.

HFO Watches/Warnings/Advisories

Flood Watch from 3 PM HST this afternoon through late tonight for Niihau and Kauai.
High Surf Advisory until 6 PM HST this evening for east facing shores of Kauai, Oahu, Molokai, Maui, and the Big Island.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov