Hilo

Today: Scattered showers, with thunderstorms also possible after 1pm. Partly sunny, with a high near 79. Southeast wind 8 to 11 mph. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 62. Southeast wind 5 to 11 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Thursday: Scattered showers, mainly after 7am. Partly sunny, with a high near 80. South southeast wind 5 to 9 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Scattered showers and thunderstorms after noon. Partly sunny, with a high near 80. Light west northwest wind. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Partly cloudy, with a low around 61. Light and variable wind.

Thursday: Scattered showers after noon. Partly sunny, with a high near 81. Light south southwest wind. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Waimea

Today: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 76. Light and variable wind. Chance of precipitation is 30%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Partly cloudy, with a low around 49. East wind 3 to 5 mph.

Thursday: Scattered showers after noon. Mostly sunny, with a high near 77. Light west wind. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Kohala

Today: Isolated showers, then scattered showers and thunderstorms after noon. Partly sunny, with a high near 74. West southwest wind around 5 mph. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Partly cloudy, with a low around 40. Light south wind.

Thursday: Scattered showers, mainly after noon. Mostly sunny, with a high near 74. Light and variable wind. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Scattered showers, mainly before noon. Mostly sunny, with a high near 79. Breezy, with an east wind around 17 mph, with gusts as high as 22 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Partly cloudy, with a low around 70. Breezy, with an east northeast wind around 18 mph, with gusts as high as 23 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Thursday: Scattered showers, mainly before noon. Mostly sunny, with a high near 80. Breezy, with an east wind around 18 mph, with gusts as high as 23 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Puna

Today: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 78. South southeast wind around 11 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. Mostly cloudy, with a low around 60. South southeast wind around 7 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Thursday: Scattered showers. Partly sunny, with a high near 79. Southeast wind 6 to 8 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Waikoloa

Today: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 82. West northwest wind around 6 mph. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Mostly clear, with a low around 59. East southeast wind 3 to 7 mph.

Thursday: Scattered showers after noon. Mostly sunny, with a high near 82. West wind 3 to 7 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Detailed Forecast

Synopsis

Winds have weakened and turned southerly ahead of an approaching cold front northwest of Kauai. Expect increasing showers to form along a cloud band, impacting mainly Oahu and Kauai through Thursday. The rest of the state will see passing showers with embedded brief downpours, mixed with periods of benign weather and clear skies.

Discussion

A front about 150 miles northwest of Kauai has turned island winds from the south. Convergence in the southerly flow has created a band of overcast skies over the Kauai Channel with scattered showers mainly impacting western Oahu. Small movement of this band to the east would bring large changes in the weather for Oahu in the form of clouds and widespread rain. The forecast for today increases showers over Oahu, with a focus on the western locations on the island. The Big Island Puna and Kau districts will see quick hitting showers through the morning as they ride the southeast flow into the Mauna Loa slopes. Some increased convection is expected on the Big Island lower slopes this afternoon with the potential for an isolated thunderstorm or two.
Satellite estimated precipitable water (PW) from CIMSS shows increasing PW moving over the eastern half of the state and reaching toward Oahu. This moisture paired with the low level convergence, and slight instability aloft should bring increasing rainfall along the convergence band. High resolution models depict this convergence band remaining in the vicinity of Oahu through Thursday as the front weakens to a trough as it reaches Kauai. Expect organized showers to form along the convergence band near Oahu, while the rest of the state sees scattered showers with embedded downpours. Away from the band there will also be plenty of periods of benign weather and clear skies.
Friday, high pressure to the northeast is expected to build in trade winds from east to west across the state. Current model solutions place a remnant trough near Oahu Thursday night that will push westward with the trades Friday. This scenario would bring increasing showers to Kauai, while the rest of the state transitions to a trade wind regime. Over the weekend, expect breezy trade winds and mainly windward showers.

Aviation

Light winds, ahead of a front approaching the islands from the northwest, will veer to southerly and southwesterly during the forecast period. This will focus clouds and showers over southern and mauka areas where isolated instances of MVFR are possible. Isolated thunderstorms are possible across the Big Island interior this afternoon. A prefrontal band of showery low clouds lies between Oahu and Kauai this morning. More organized shower activity and a greater probability of MVFR can be expected for the western islands through today.
No AIRMETs are in effect now, but may be needed later this morning as the showery cloud band in the Kauai Channel becomes more active and affects the nearby islands.

Marine

A cold front approaching will move over the Kauai and Oahu waters tonight into Thursday, then stall and diminish by Thursday night. Winds will vary from the south-southwest direction over the Kauai and Oahu waters to south-southeast over the Maui County and Big Island waters out ahead of the front. Pockets of fresh breezes can be expected within the southeast flow near South Point of the Big Island and over the Big Island windward waters along the Hamakua coast. Light and variable winds will be possible over the Kauai and Oahu waters tonight through Thursday as the front moves into the area. In addition to the winds, shower coverage along and ahead of the front will increase through the day, especially over the western end of the state (few storms can’t be ruled out today across the Kauai/Oahu waters). Fresh to locally strong easterly trade winds are expected to return Friday through the weekend as the trough shifts west of the area and the ridge builds to the north.
Surf along exposed north and west facing shores will trend up today and hold through Thursday as a moderate northwest (320 deg) swell builds down the island chain. Overnight observations from the offshore and nearshore buoys reflect this new energy increasing within the 14 to 15 second bands. Surf will near advisory levels at its peak this afternoon through Thursday for the smaller islands, then ease over the weekend. For the long range, guidance depicts a broad gale developing and lifting northward over the far northwest Pacific near the Kurils this weekend, which could send a small, long-period west-northwest swell into the area by Wednesday of next week (low confidence).
Surf along east facing shores will remain up just below the advisory level through Thursday due to a background easterly trade wind swell from a large area of fresh breezes upstream of the islands. A downward trend will be possible over the weekend.
Surf along south facing shores will trend up through the second half of the week and into the weekend as overlapping, long-period south- southwest swells move through from recent activity across the southern Pacific within Hawaii’s swell window.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov