Hilo

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 70 near the shore to around 55 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 70 percent.

Sunday: Partly sunny. Scattered showers early in the morning, then scattered showers and slight chance of thunderstorms in the late morning and afternoon. Highs 80 to 86 near the shore to 65 to 70 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the evening, then numerous showers in the late evening and overnight. Lows 63 to 71 near the shore to around 55 at 4000 feet. East winds up to 10 mph shifting to the south after midnight. Chance of rain 70 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 73 near the shore to 48 to 53 near 5000 feet. Light winds. Chance of rain 50 percent.

Sunday: Mostly sunny with isolated showers early in the morning, then partly sunny with numerous showers and slight chance of thunderstorms in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs 83 to 88 near the shore to around 67 near 5000 feet. West winds up to 10 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy early in the evening then becoming partly cloudy. Numerous showers and slight chance of thunderstorms early in the evening, then isolated showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows around 73 near the shore to 48 to 53 near 5000 feet. Light winds. Chance of rain 70 percent.

Waimea

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday: Breezy. Mostly sunny with isolated showers early in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the late morning and afternoon. Highs 65 to 85. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday: Breezy. Mostly sunny with isolated showers early in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the late morning and afternoon. Highs 65 to 85. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows around 74 near the shore to around 52 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Sunday: Breezy. Sunny early in the morning, then partly sunny with numerous showers and slight chance of thunderstorms in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs around 86 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy early in the evening then becoming mostly clear. Numerous showers and slight chance of thunderstorms early in the evening. Locally heavy rainfall possible early in the evening. Lows around 74 near the shore to around 52 near 5000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Puna

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 70 near the shore to around 55 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 70 percent.

Sunday: Partly sunny. Scattered showers early in the morning, then scattered showers and slight chance of thunderstorms in the late morning and afternoon. Highs 80 to 86 near the shore to 65 to 70 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the evening, then numerous showers in the late evening and overnight. Lows 63 to 71 near the shore to around 55 at 4000 feet. East winds up to 10 mph shifting to the south after midnight. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows around 74 near the shore to 50 to 55 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 40 percent.

Sunday: Sunny early in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the late morning and afternoon. Highs 84 to 89 near the shore to 66 to 73 above 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy. Scattered showers and slight chance of thunderstorms early in the evening. Lows 71 to 76 near the shore to 50 to 55 above 4000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Gentle to moderate trade winds will continue for the rest of the weekend, bringing a few showers to windward areas. Additionally, afternoon sea breezes will bring clouds and showers to leeward and interior areas. A low aloft will destabilize the island atmosphere, supporting the potential for some locally heavy showers and a slight chance of thunderstorms, first for Kauai and Oahu (including surrounding waters) tonight, then gradually spreading to the remainder of the state by Sunday. Stronger trade winds and increasingly stable conditions will return next week.

Discussion

Prevailing background winds across the islands have been in the gentle to moderate range today as a result of a weakened Northeast Pacific High far north of the state. These gentle to moderate background trade winds winds will remain in place throughout the rest of the weekend. Meanwhile, local satellite and radar imagery shows that low-level convergence has resulted in afternoon sea breeze induced showers across select leeward areas.
Some tweaks have been made to rain and thunder chances through the rest of the weekend based on latest National Blend of Models, ECMWF, and GFS guidance with this afternoon's forecast updates, but the overall forecast philosophy remains unchanged. For the rest of the weekend, a low aloft will shift southward, eventually settling over the central islands on Sunday. This low will destabilize the atmosphere and increase vorticity aloft as 500mb temperatures cool to around -11C. As inversion heights increase, expect taller cloud development and heavier showers. Additionally, the increasing instability will support slight chances of thunderstorms that will include Kauai and Oahu tonight, then spreading to the remaining islands on Sunday, including the slopes of the Big Island Sunday afternoon.
Given the relatively light background flow, afternoon sea breezes are expected along select leeward areas again on Sunday. The heavier showers will be most likely over leeward areas during the afternoon and evening periods, and over windward areas during the overnight and morning hours. The caveat to the forecast, however, is that precipitable water values are expected to be near the 1.2 to 1.5 inch range, which is very close to normal for early October. Therefore, although there should be sufficient moisture for a few heavier showers and perhaps isolated thunderstorms, the amount of moisture available is not significantly higher than what is to be expected for this time of year.
Models still show trade winds gradually increasing as early as late Sunday into early next week as a new high pressure to the distant northwest builds eastward. Stability will also increase as the low aloft weakens and moves away to the northeast. Some instability may linger through Monday, but generally, increasingly stable trade wind conditions should return by Tuesday and persist through much of next week. With the return of a more typical trade wind pattern, expect clouds and showers to favor primarily windward and mauka areas.

Aviation

Light to moderate trade winds will continue this weekend, with afternoon sea breezes developing over terrain-sheltered leeward areas. A developing upper-level low over the islands will increase low cloud and shower coverage through at least Sunday, favoring windward areas overnight and leeward/inland areas in the afternoons. VFR conditions are expected to prevail, with periods of MVFR and isolated IFR conditions possible in the heavier showers. There is also a slight chance of thunderstorms over the eastern half of the state tonight, then state-wide through the weekend, due to increasing instability from the low aloft.
No AIRMETs are currently in effect. AIRMET Sierra may be needed tonight if low clouds and showers become widespread enough to obscure island terrain.

Marine

The ridge to the northeast of the islands has weakened further, leaving gentle to locally moderate trades across the region. An upper level low has moved into the offshore waters to the northeast of the islands, and is about 170 nm northeast of Kauai this afternoon. The global models show this upper level feature strengthening as is sinks southward in the next 24 hours. Although no thunderstorms have yet been observed, the chance for thunderstorms remains in the forecast for the offshore and coastal waters near the upper low through tomorrow afternoon. By tomorrow night, the low is forecast to lift back to the north.
A surface ridge looks to start forming to the north of the islands tomorrow, which will help the trades to begin to become re- established across the region. By Monday morning, Small Craft Advisory (SCA) level winds are possible in the typical windier coastal waters near Maui County and the Big Island. Once SCA winds return, we can expect those to continue through at least mid-week.
A pair of overlapping small, short period north swells should maintain small surf across north facing shores through the remainder of the weekend. A short lived small, short to medium period northeast swell is expected through tomorrow, which will also boost surf along east facing shores. There is the potential for a moderate long period north-northwest swell as early as tomorrow, which would peak Monday below advisory levels for north facing shores, with the swell lingering into the middle of the new week.
A moderate, long period south swell hasn't shown on the near shore buoys yet, and the latest guidance now indicates it should arrive later this evening. Expect this to then fill in tonight, peaking perhaps a little later tomorrow, hold into Monday, and then gradually declining through the middle of next week. This swell may boost surf along south facing shores to near or slightly below advisory levels during its peak.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov