Hilo

Today: Isolated showers. Mostly sunny, with a high near 76. West northwest wind around 6 mph becoming calm in the afternoon. Chance of precipitation is 20%.

Tonight: Scattered showers. Mostly cloudy, with a low around 59. Calm wind becoming west southwest around 6 mph after midnight. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 77. East wind 5 to 7 mph becoming light and variable in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Kona

Today: Scattered showers after 1pm. Widespread haze after 1pm. Increasing clouds, with a high near 78. East northeast wind around 6 mph becoming west southwest in the afternoon. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers before 1am. Widespread haze. Mostly cloudy, with a low around 58. Calm wind becoming south around 6 mph after midnight. Chance of precipitation is 40%. New precipitation amounts between a quarter and half of an inch possible.

Sunday: Scattered showers and thunderstorms after 1pm. Widespread haze. Mostly sunny, with a high near 79. South wind 5 to 7 mph becoming west in the afternoon. Chance of precipitation is 30%. New rainfall amounts between a quarter and half of an inch possible.

Waimea

Today: Isolated showers after noon. Mostly sunny, with a high near 73. Northeast wind 5 to 10 mph becoming light and variable in the afternoon. Chance of precipitation is 20%.

Tonight: Scattered showers, mainly after midnight. Partly cloudy, with a low around 49. Calm wind becoming south southwest around 6 mph after midnight. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Isolated showers, then scattered showers and thunderstorms after noon. Mostly sunny, with a high near 74. West northwest wind 5 to 7 mph becoming light and variable in the afternoon. Chance of precipitation is 30%. New rainfall amounts between a half and three quarters of an inch possible.

Kohala

Today: Isolated showers after noon. Mostly sunny, with a high near 69. Southwest wind around 6 mph becoming light and variable in the afternoon. Chance of precipitation is 20%.

Tonight: Scattered showers. Mostly cloudy, with a low around 41. Southwest wind 3 to 6 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 70. West southwest wind 5 to 7 mph becoming light and variable in the afternoon. Chance of precipitation is 30%. New rainfall amounts between a half and three quarters of an inch possible.

South Big Island

Today: Widespread haze after noon. Mostly sunny, with a high near 78. Breezy, with an east wind 9 to 16 mph, with gusts as high as 21 mph.

Tonight: Isolated showers before midnight. Widespread haze. Partly cloudy, with a low around 66. East wind 6 to 9 mph. Chance of precipitation is 20%.

Sunday: Isolated showers and thunderstorms after noon. Widespread haze. Mostly sunny, with a high near 79. Southeast wind 5 to 7 mph becoming light and variable in the afternoon. Chance of precipitation is 20%.

Puna

Today: Scattered showers, mainly after noon. Mostly sunny, with a high near 75. Northwest wind 5 to 7 mph becoming northeast in the afternoon. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 58. North northwest wind around 6 mph. Chance of precipitation is 50%. New precipitation amounts between a quarter and half of an inch possible.

Sunday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 76. North northwest wind 5 to 7 mph becoming east in the morning. Chance of precipitation is 50%. New rainfall amounts between three quarters and one inch possible.

Waikoloa

Today: Isolated showers after noon. Mostly sunny, with a high near 79. East wind 5 to 10 mph becoming light and variable in the afternoon. Chance of precipitation is 20%.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 58. Light and variable wind becoming south southwest around 6 mph after midnight. Chance of precipitation is 20%.

Sunday: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 80. South southwest wind 5 to 7 mph becoming north in the afternoon. Chance of precipitation is 40%. New rainfall amounts between a half and three quarters of an inch possible.

Detailed Forecast

Synopsis

Light winds will prevail statewide today, with moderate northeast trade winds redeveloping over Kauai and Oahu on Sunday, then gradually strengthening statewide early next week. A period of unsettled weather is possible tonight through Monday, as a potent low aloft passes over the area, bringing the potential for thunderstorms, and a few locally heavy downpours. A more settled weather pattern is expected thereafter.

Discussion

A high to the distant N and a persistent low to the NE of the islands are maintaining light to locally moderate NE trade winds over western parts of the chain this morning, with lighter winds over the E end of the chain. Satellite and radar indicate that showers remain widely separated, but have increased in coverage and intensity ever so slightly. Overnight soundings shows an increase in PWAT to near 1.2″, with a robust subsidence inversion still intact near 9000′. Otherwise, scattered high clouds are moving from W to E while dew points in the upper 50s to lower 60s F have allowed overnight low temperatures to drop into the lower- to mid-60s F.
The low-level pressure gradient near and NE of the islands will become quite weak today as troughing to the distant NE drifts W and (partially) moves between the islands and the trade-wind-supporting high. Light and variable winds will develop over Maui and the Big Island with light NE winds over Kauai and Oahu, with a few windward showers expected this morning. Winds will be sufficiently light statewide to allow afternoon sea breezes to drive some cloud formation over leeward and interior portions today. There is some uncertainty as to how unstable the island atmosphere will become in the short term as a developing shortwave trough approaches from the N, but the forecast calls for scattered showers.
A potent shot of mid-level cold air is expected to accompany the aforementioned shortwave trough aloft that will sharpen as it moves over the islands tonight through Monday. This will significantly destabilize the island atmosphere as mid-level temperatures plummet from -8C to -16C, but PWAT will remain on the lower side (near 1.2″). Locally derived guidance depicts thunderstorm chances steadily increasing tonight, peaking Sunday, then slowly diminishing and shifting E on Monday. While instability will be high, allowing thunderstorms and a few heavy rain cells to develop, the relatively low PWAT will likely preclude the threat of widespread heavy rainfall that would lead to significant flooding.
Periods of wintry weather will be possible over the Big Island Summits and upper slopes with any deeper convection that develops, and the freezing level may become low enough to support a brief period of wintry weather over the summit of Haleakala – with the most likely time being Sunday/Sunday night.
Models indicate surface low pressure will linger NE of the islands into the middle of next week, leading to moderate NE winds over Kauai and Oahu, and lighter NE winds over Maui County and the Big Island, with mostly dry and stable conditions in place. A weak cold front may move into the area from the N around Thursday.

Aviation

A light to moderate trade wind flow will persist through tonight. The weakness of this flow and daytime heating will lead to local daytime sea breeze over the interior and lee areas of the smaller islands, resulting in some afternoon clouds and possibly a few showers. Leeward Big Island faces a similar scenario this afternoon as well. This trade wind flow will take on a more northeast component as the day progresses, and continue through Sunday.
Thus far, trade wind clouds and showers are affecting mainly the windward and mountain areas, causing brief periods of MVFR ceiling and vis. Tops of these showers are around 8k feet, with higher tops to 12k feet in the stronger showers. Look for the frequency of these showers to become less by mid morning. VFR will be primary flying weather for today.
A strong upper level disturbance will be coming in tonight from the north, leading to a slight chance for a thunderstorm, especially over the eastern part of the island chain.
No AIRMETS, and none are expected through this afternoon.

Marine

Moderate northeast trade winds will trend down through the weekend as the ridge weakens to the north. Winds should become light enough for a land and sea breeze regime to setup for most areas. The background flow will shift out of a more northerly direction (stronger Kauai and Oahu waters) due to a persistent trough/low lurking northeast of the state. In addition to light winds, a few heavy showers and thunderstorms will become a possibility tonight through Sunday as an upper disturbance drops south over the islands – best chance windward waters and eastern half of the state. Northeast trade winds will gradually return early next week, potentially reaching the fresh to locally strong category by midweek.
Surf along south facing shores will gradually rise over the weekend as a long-period, south-southwest swell arrives from recent activity within Hawaii’s swell window near New Zealand. This source should be fully filled in by Monday, then hold into midweek before lowering. Heights should peak just below the advisory threshold (8 ft faces) early next week.
Surf along north and west facing shores will remain small through the weekend, then trend up late Sunday through early next week as a small, west-northwest swell arrives from a gale that developed near the Kurils earlier this week. Although confidence remains low, a moderate, short-period north-northeast swell is depicted late next week due a strong gradient setting up once again to the north between strong high pressure near the Date Line and low pressure to its east.
Surf along east facing shores will lower over the weekend as the persistent north-northeast swell fades and the local winds diminish. Surf will remain small early next week, then trend up by the second half along exposed coasts as the previously discussed north- northeast swell arrives.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov