Photo Credit: James Grenz

Hilo

Today: Scattered showers, then showers likely and possibly a thunderstorm after 1pm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 78. Calm wind becoming west southwest around 5 mph. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely and possibly a thunderstorm before 9pm, then scattered showers. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 63. Light east southeast wind. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Scattered showers, then showers likely and possibly a thunderstorm after 1pm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 77. Calm wind becoming east around 6 mph in the afternoon. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Isolated showers, then scattered showers and thunderstorms after noon. Mostly cloudy, with a high near 79. East northeast wind around 5 mph becoming calm. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers and thunderstorms before 8pm, then isolated showers. Mostly cloudy, with a low around 61. North northwest wind around 5 mph becoming calm in the evening. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Isolated showers, then scattered showers and thunderstorms after noon. Partly sunny, with a high near 79. Light and variable wind. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Waimea

Today: Isolated showers, then scattered showers and thunderstorms after noon. Mostly cloudy, with a high near 74. North northeast wind 3 to 7 mph. Chance of precipitation is 40%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Scattered showers and thunderstorms before 8pm, then isolated showers. Mostly cloudy, with a low around 52. North northeast wind around 5 mph becoming calm after midnight. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Isolated showers, then showers likely and possibly a thunderstorm after noon. Some of the storms could produce heavy rainfall. Partly sunny, with a high near 74. Light and variable wind. Chance of precipitation is 60%. New rainfall amounts between a half and three quarters of an inch possible.

Kohala

Today: Isolated showers, then scattered showers and thunderstorms after noon. Mostly cloudy, with a high near 70. Light northeast wind. Chance of precipitation is 40%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms before 8pm, then isolated showers. Mostly cloudy, with a low around 45. Calm wind becoming northeast around 5 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Friday: Isolated showers, then showers likely and possibly a thunderstorm after noon. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 70. Calm wind becoming west southwest 5 to 7 mph in the afternoon. Chance of precipitation is 60%. New rainfall amounts between a quarter and half of an inch possible.

South Big Island

Today: Scattered showers, with thunderstorms also possible after noon. Mostly cloudy, with a high near 79. Breezy, with an east northeast wind 11 to 17 mph, with gusts as high as 21 mph. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 69. East northeast wind 11 to 13 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Friday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 79. East northeast wind 7 to 13 mph. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Puna

Today: Showers likely, with thunderstorms also possible after noon. Some of the storms could produce heavy rainfall. Cloudy, with a high near 76. Light and variable wind becoming south southwest around 5 mph. Chance of precipitation is 60%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Cloudy, with a low around 61. Calm wind becoming southeast around 6 mph after midnight. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Friday: Showers likely, with thunderstorms also possible after noon. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 76. West northwest wind 5 to 9 mph becoming southeast in the afternoon. Chance of precipitation is 60%. New rainfall amounts between a half and three quarters of an inch possible.

Waikoloa

Today: Isolated showers, then scattered showers and thunderstorms after noon. Mostly cloudy, with a high near 80. East wind around 6 mph becoming northwest in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers and thunderstorms before 8pm, then isolated showers. Mostly cloudy, with a low around 61. North northwest wind around 5 mph becoming calm in the evening. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Isolated showers, then scattered showers and thunderstorms after noon. Partly sunny, with a high near 80. West northwest wind around 5 mph becoming calm in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Detailed Forecast

Synopsis

A wet pattern could linger into the weekend as deep tropical moisture pools northward over the state in response to low pressure west of the area. Saturated grounds and elevated water levels in streams will keep the threat for flash flooding up across the state through Friday, especially over the western end. Light to moderate southerly winds will hold through Friday, then shift out of the north-northeast and become strong over the western end of the state by Saturday as high pressure builds to the north behind a cold front.

Discussion

Deep tropical moisture pooling northward across the state due to an upper trough and surface low positioned to the west will keep the threat for heavy rainfall and flash flooding in the forecast through Friday. Although the threat for localized flooding will remain in place statewide, the best chance will remain over Oahu and Kauai where the better instability is located. As a result, the Flash Flood Watch (FFA) remains in effect through 6 PM HST Friday statewide. In addition to the rainfall, the aforementioned instability associated with the upper trough will be enough to trigger thunderstorms periodically. Guidance depicts the low- level flow remaining in the light to moderate range out of the southerly direction into tonight, then shifting out of the southwest Friday as the surface low to the west begins to lift off to the northeast. Winds should be light enough to keep the land and sea breeze pattern in place through this time.
The extended guidance shows the surface low lifting off to the northeast this weekend as a shortwave trough dives southeastward into the area and a cold front passes to the north. Strong high pressure (1040 mb) building to the north in the wake of the front will translate to strong north-northeast winds over the western end of the state beginning Friday night/Saturday. Light winds, however, may linger over the eastern end of the state as the tail- end of the front stalls nearby to the north of the Big Island. Forecast confidence diminishes for early next week due to large differences shown between model solutions.

Aviation

Showers and thunderstorms are increasing in coverage as they spread east over Kauai. Meanwhile, showers have recently increased in coverage over Oahu primarily impacting PHNL and vicinity. AIRMET Sierra was recently expanded to include Oahu in addition to Kauai. A threat for MVFR and organized heavy rainfall, including isolated thunderstorms, will continue through the forecast period. Further, moist onshore has begun to produce an expansion of showers over portions of Big Island where AIRMET Sierra may eventually be required for sections of the windward and southeast-facing slopes. Wind will remain light and out of the southeasterly quadrant through the forecast period.

Marine

A low pressure system over the western offshore waters will produce southerly to variable winds across regional waters through Friday. A cold front will move into the northern offshore waters Friday into Saturday. The low will merge with the approaching cold front and this will enhance showers and thunderstorms into the weekend. Strong north to northeast winds will develop northwest of the front, near Kauai and Oahu, as a strong high builds into the local waters from Friday night into Saturday.
A High Surf Advisory (HSA) remains in effect for the east facing shores of Kauai, Oahu, Molokai, Maui and the Big Island through 6 PM this evening. The Small Craft Advisory was cancelled this morning due to lowering seas.
An elevated east swell will keep surf heights in the HSA range today along east facing shores today. This east swell will gradually lower from tonight through Friday. Small surf will continue along north and west facing shores through Friday. Surf heights along east facing shores will quickly rise and may reach warning levels Saturday and Sunday due to a combination of strong trades returning over the Kauai and Oahu waters and a medium period north swell arriving. Surf could reach advisory levels for north facing shores during this time. This swell will slowly decline from Sunday night into Tuesday. A small background south to southwest swell will keep surf small along most south facing shores with a small bump expected on Thursday and Friday.

HFO Watches/Warnings/Advisories

Flash Flood Watch through Friday afternoon for all Hawaii islands.
High Surf Advisory until 6 PM HST this evening for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, South Big Island, Big Island North and East.

Data Courtesy of NOAA.gov