Hilo

Today: Mostly cloudy with numerous showers and isolated thunderstorms. Highs 75 to 81 near the shore to around 65 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 64 to 70 near the shore to around 55 at 4000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 83 near the shore to around 66 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Kona

Today: Partly sunny with scattered showers and isolated thunderstorms. Highs 81 to 87 near the shore to around 65 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers and thunderstorms. Lows around 73 near the shore to 48 to 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 66 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Waimea

Today: Partly sunny with isolated showers and thunderstorms. Highs 71 to 78 near the shore to 65 to 76 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 63 to 69 near the shore to 56 to 61 near 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 73 to 80 near the shore to 66 to 76 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Kohala

Today: Partly sunny with isolated showers and thunderstorms. Highs 71 to 78 near the shore to 65 to 76 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 63 to 69 near the shore to 56 to 61 near 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 73 to 80 near the shore to 66 to 76 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly sunny with isolated showers and thunderstorms. Highs around 83 near the shore to around 64 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers and thunderstorms. Lows around 72 near the shore to around 50 near 5000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 84 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Puna

Today: Mostly cloudy with numerous showers and isolated thunderstorms. Highs 75 to 81 near the shore to around 65 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 64 to 70 near the shore to around 55 at 4000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 83 near the shore to around 66 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Today: Partly sunny with numerous showers and isolated thunderstorms. Highs 81 to 86 near the shore to 64 to 70 above 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Tonight: Partly cloudy with isolated showers and thunderstorms. Lows around 73 near the shore to 51 to 56 above 4000 feet. East winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 86 near the shore to 65 to 71 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Heavy rain and isolated thunderstorms are possible over all islands again today. The threat will diminish by tonight and a land and sea breeze pattern favoring clouds and showers over island interiors will continue into the middle of next week. Another low will bring the threat of heavy rain to the islands during the second half of next week.

Discussion

Local radar composite loop hints at the present state of the middle and upper atmosphere as heavy showers and thunderstorms rotate cyclonically around the area. Heavy rain up to 3″/hour lifting northeastward over northern Big Island has recently dissipated while a fresh round of heavy showers developed and moved over Kauai from the north this morning. In between, steering flow remains rather nebulous and slow-moving showers and thunderstorms have developed off the windward coasts of Oahu and Molokai. The onset of daytime heating will allow these showers to redevelop inland. Worth noting that all guidance has quite a poor handle on the current distribution of precipitation across the state this morning. The Flood Watch remains in effect for the islands through today.
Focus for today will shift toward another west-east progression of heavy rain potential as a shortwave embedded within the parent low aloft pivots through the area during the next 12-18 hours. The thermal trough associated with this second wave is of similar magnitude to yesterday's, if not slightly colder (-14 to -16C at 500mb). 700-500mb lapse rates over Kauai have almost certainly steepened from this morning's 12z sounding and are probably solidly in excess of 7.0 C/km. This favorable environment for deep convective growth leading to heavy showers and isolated thunderstorms will sweep eastward as the day progresses. Heavy rain leading to flash flooding will be a possibility for all islands once again today.
The resident upper low will very gradually reabsorb into the baroclinic westerlies during the next few days leaving the islands firmly within the trailing envelope of cyclonic flow aloft, though forcing and instability will diminish. In the near term (Sunday into Monday), the established airmass will remain in place with continued weak troughing over the islands supporting a light easterly gradient and the consequent land and sea breeze pattern. This will favor afternoon cloud build ups and interior showers of less intensity than those of yesterday and today.
Strong consensus exists among the global models that high amplitude mid-latitude troughing will beget another closed low in the vicinity of the islands during the middle of next week. The local gradient responds to the associated height falls as early as Monday-Tuesday when surface winds veer to southeasterly and advect higher dewpoints (near 70F) into the region. In addition to the lack of meaningful wind and increasingly uncomfortable humidity, this will supply plenty of boundary layer moisture for afternoon showers as the sea breeze pattern continues.
The second half of next week bears watching as the aforementioned closed low reaches its southernmost extent. Current consensus indicates PWATs rising toward 2″ as convergent southwesterly flow establishes over the islands leading to an elevated heavy rain threat. The inherited forecast handles this potential well, including the risk of thunderstorms.

Aviation

A strong upper level disturbance will continue to gradually move eastward across the state today. As a result, enhanced shower activity and isolated thunderstorms will produce periods of MVFR and local IFR. Light winds should allow for sea breeze development this afternoon, with scattered showers possible over the interior and sheltered leeward areas.
AIRMET Sierra for tempo mountain obscuration is in effect for all of Kauai and windward portions of Oahu this morning. This AIRMET will likely be needed on and off throughout the day for portions of island chain as showers develop and dissipate.
AIRMET Tango for moderate to isolated severe mid to upper level turbulence remains in effect as the upper level disturbance moves across the state. Conditions will likely improve heading into the evening hours.
AMD NOT SKED for PMDY continues due to equipment issues, with no timeline for restoration.

Marine

Thunderstorms, some of which could be strong to severe, will remain possible across Hawaiian coastal waters today as an upper disturbance moves across the area. Any thunderstorms that develop will have the potential to produce gusty winds, small hail, and frequent lightning. Marine interests should continue to monitor for any Special Marine Warnings that may be issued. Light and variable winds will prevail today, except within and near thunderstorms. Light to moderate easterly trade winds will begin building back into the region on Sunday. Winds will weaken again and become more southerly by Monday night as high pressure becomes established both far northeast and far northwest of the islands and a trough in between moves into the region.
Surf along south facing shores remains elevated, but will slowly decline through Sunday and then hold into early next week as a long-lived, small south swell continues to affect the islands. Although the swell size itself will remain largely unchanged through Sunday night, the period will gradually shorten from 15 seconds today to near 13 seconds by Sunday night, allowing surf heights to slowly trend down. Another series of overlapping, long-period south swells will begin moving in on Tuesday, with reinforcements giving another noticeable boost to south shore surf from Wednesday through the rest of next week.
A small, short-period north-northwest swell has increased north shore surf this morning, but this will decline later today into Sunday. A new small, long-period northwest swell will build Sunday night, giving north shore surf a boost early next week. Surf along east facing shores will be well below normal levels through the middle of next week.

HFO Watches/Warnings/Advisories

Flood Watch through this evening for all Hawaiian Islands.
Wind Advisory until 6 PM HST this evening for Big Island Summits.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.

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Data Courtesy of NOAA.gov