Hilo

Today: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 80 to 87 near the shore to 65 to 74 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely. Lows 65 to 74 near the shore to around 58 at 4000 feet. North winds 10 to 15 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Monday: Showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 79 to 86 near the shore to 63 to 70 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Kona

Today: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 84 to 90 near the shore to around 71 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Isolated showers. Lows 72 to 77 near the shore to 50 to 56 near 5000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then cloudy with showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 85 to 90 near the shore to around 71 near 5000 feet. Northeast winds up to 10 mph shifting to the southwest around 10 mph in the afternoon. Chance of rain 70 percent.

Waimea

Today: Partly sunny with scattered showers. Highs around 81 near the shore to 69 to 80 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 65 to 73 near the shore to 56 to 64 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Occasional showers and slight chance of thunderstorms in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 81 near the shore to 69 to 80 near 3000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Kohala

Today: Partly sunny with scattered showers. Highs around 81 near the shore to 69 to 80 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 65 to 73 near the shore to 56 to 64 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Occasional showers and slight chance of thunderstorms in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 81 near the shore to 69 to 80 near 3000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

South Big Island

Today: Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 87 near the shore to around 70 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Lows around 75 near the shore to around 53 near 5000 feet. Southeast winds around 10 mph shifting to the northeast after midnight. Gusts up to 30 mph.

Monday: Breezy. Mostly sunny with isolated showers in the morning, then cloudy with showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 87 near the shore to around 70 near 5000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Puna

Today: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 80 to 87 near the shore to 65 to 74 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely. Lows 65 to 74 near the shore to around 58 at 4000 feet. North winds 10 to 15 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Monday: Showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 79 to 86 near the shore to 63 to 70 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Waikoloa

Today: Mostly sunny. Highs 85 to 90 near the shore to 67 to 74 above 4000 feet. Northeast winds 10 to 15 mph shifting to the northwest in the afternoon.

Tonight: Partly cloudy. Scattered showers after midnight. Lows around 75 near the shore to 51 to 58 above 4000 feet. Northeast winds 10 to 15 mph shifting to the east after midnight. Chance of rain 40 percent.

Monday: Mostly sunny with scattered showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs 85 to 91 near the shore to 67 to 74 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate trade winds deliver a few clouds and showers to windward areas today, while leeward areas remain mostly dry. Tropical moisture associated the remnants of Fernanda will move over the state on Monday, bringing locally heavy rainfall to windward areas of the Big Island, and potentially Maui County. Windward areas of Oahu and Kauai will also receive some showers. Little significant rainfall is expected over most leeward areas, including leeward Maui. A trend toward breezy and increasingly dry trade wind weather is expected to begin on Tuesday.

Discussion

Satellite imagery shows an overnight increase in low cloud coverage over both windward and leeward waters, with radar indicating a modest increase in shower coverage. A few showers are moving into windward areas, some with small cores of heavier rain, moving too quickly to provide much relief from the recent dry conditions. Model analyses indicate the local increase in low cloud cover is related to the passage of a low-level trough to the N of the islands. Water vapor imagery shows a broad low aloft centered just S of the Big Island, with this feature drifting N toward the islands. The center of the remnant circulation of Tropical Cyclone Fernanda is about 500 miles ESE of Hilo, tracking toward the W near at 15 to 20 mph. The associated field of increased moisture (PWAT > 2″) extends outwards up to 200 miles N of the center, about 300 miles to the E.
The short-term forecast anticipates moderate trade winds that will likely allow localized leeward sea breezes to develop this afternoon. A few showers will move into windward areas, especially this morning, with fewer showers by the afternoon as the effects of the passing surface trough wane. While generally benign weather will prevail today, it looks to be a little cloudier and wetter than the past couple of days, especially windward. Most leeward areas will remain dry, including leeward Maui.
Model guidance continues to indicate that the bulk of the moisture associated with Fernanda's remnant will pass S of the islands from tonight through Tuesday. However, a significant moisture surge is expected over the Big Island and Maui late tonight through Monday, bringing the potential for heavy showers, primarily over windward areas. In addition to the surge in PWAT, the low aloft (and its mid- level reflection) will be located over the islands, providing increased instability due to cooling mid-level temperatures, and divergence aloft as a negatively-trough develops. Simulated satellite imagery depicts a period of deeper convection near and over the Big Island on Monday, thus a slight chance of thunderstorms has been added to the forecast. In addition, the arrival (and temporal extent) of heavy showers over windward Maui has been time shifted to be a bit later as indicated by latest guidance.
Although the potential for heavy rain is fairly high, it should be fairly short-lived, and is not expected to lead to flash flooding. There's a good chance of nuisance-level flooding, but the threat of flash flooding is not great enough to warrant the issuance of a Flood Watch at this time. Anticipated rainfall amounts are lower over Kauai and Oahu as the increase in PWAT is not expected to be as great as that seen farther S. However, dew points rising into the lower 70's will make it feel muggy statewide.
By Tuesday the mid-level low will lift N of the area, and the trough aloft will weaken, allowing stability to increase. This will lead to drier trade wind weather, with building high pressure far NNE of the islands supporting breezy trade winds. Pronounced drying is expected by mid-week as a mid-level ridge develops over the area.

Aviation

Moderate easterly trade winds will continue, with clouds and showers favoring windward and mountain areas. Rainfall chances will trend up over the far eastern end of the state tonight through Monday as an area of deep tropical moisture approaching begins to fill in. This will translate to periods of MVFR CIGS/VSBYS for windward portions of the Big Island and Maui County.
There are currently no AIRMETs, and none are expected through this afternoon. AIRMET Sierra for mountain obscuration will become a possibility tonight into Monday for windward sections of the Big Island and Maui County.

Marine

Surface high pressure far north of the state will maintain moderate to locally fresh trade winds through tonight. As the high builds on Monday, trade winds will strengthen to locally strong speeds with a Small Craft Advisory likely for the windier waters around Maui County and the Big Island. At the same time, the remnants of Fernanda will pass south of the islands, bringing an increase in showers, especially over the windward waters Monday through Tuesday and a slight chance of thunderstorms over the Big Island waters on Monday. High pressure will remain far north of the state through the second half of next week with fresh to locally strong winds persisting.
Surf along east facing shores will remain small through the rest of the weekend due to lighter than normal trades over and upstream of the state. A long-period east swell generated by Hurricane Hilary could bring an increase in surf Monday through the middle of next week. The latest forecast guidance continues to indicate a long- period swell peaking around 3 to 4 feet Tuesday and holding through Wednesday, before quickly lowering through Thursday. Forecast confidence for this swell's details remains low due to its distant source and the compact nature of tropical cyclones. South shore surf will remain small through the weekend. A small, medium-period south to south-southeast swell arriving early next week should produce a modest increase along south facing shores.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov