Photo Credit: James Grenz

Hilo

Today: Mostly cloudy with numerous showers. Highs around 81 near the shore to 65 to 70 at 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 62 to 67 near the shore to around 51 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Mostly sunny with isolated showers. Highs around 81 near the shore to 65 to 70 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Kona

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 80 to 85 near the shore to around 65 near 5000 feet. West winds up to 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 65 to 73 near the shore to around 52 near 5000 feet. Light winds. Chance of rain 40 percent.

Sunday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 80 to 85 near the shore to around 65 near 5000 feet. Light winds. Chance of rain 30 percent.

Waimea

Today: Partly sunny. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 80 near the shore to 65 to 75 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 64 near the shore to 52 to 59 near 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

Sunday: Mostly sunny with isolated showers. Highs around 80 near the shore to 65 to 75 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Kohala

Today: Partly sunny. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 80 near the shore to 65 to 75 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 64 near the shore to 52 to 59 near 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

Sunday: Mostly sunny with isolated showers. Highs around 80 near the shore to 65 to 75 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Big Island

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 83 near the shore to around 69 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 66 near the shore to around 51 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Sunday: Breezy. Mostly sunny with isolated showers. Highs around 83 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Puna

Today: Mostly cloudy with numerous showers. Highs around 81 near the shore to 65 to 70 at 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 62 to 67 near the shore to around 51 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Mostly sunny with isolated showers. Highs around 81 near the shore to 65 to 70 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Waikoloa

Today: Mostly sunny with isolated showers. Highs around 84 near the shore to 66 to 72 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 66 to 73 near the shore to 48 to 55 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 84 near the shore to 66 to 72 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The weather pattern changes after this weekend as the high pressure ridge far northeast of the islands weakens and a trough approaches the region from the west. Moderate to locally breezy trade winds will veer more from the southeast direction from Sunday through Tuesday with decreasing trade wind speeds allowing local scale land and sea breezes to develop. Wind directions will veer from a more southerly direction over the western islands from late Tuesday through Thursday as the trough approaches Kauai. Deeper moisture advecting in from the south will increase chances for shower activity over Kauai and Oahu during this time period. Maui and Hawaii Counties will see continued land and sea breezes through Thursday with more stable easterly trade winds returning to the eastern half of the state by next Friday.

Discussion

The satellite imagery this morning around the Hawaiian Islands continues to show bands of clouds drifting westward on the trade winds into the windward sections of all islands. Expect some of these enhanced cloud bands to produce brief periods of showers over windward and mountain slopes of each island through the morning hours. Elsewhere a cold frontal system currently near Midway Island will continue to drift towards the Hawaii region bringing a change in the wind and weather pattern from Monday onward.
In the big picture we see a high pressure system far northeast of the island chain with a ridge extending just north of the region. Moderate to locally breezy easterly trade winds moving out of this ridge will continue to blow through the region this weekend. By Sunday this high pressure system will weaken as a low pressure system approaches the region from the west causing wind directions to shift from a more east to southeasterly direction. This southeast wind shift will produce lighter winds for the smaller islands, from Maui to Kauai, as the Big Island produces a blocking wind shadow effect over these areas. As large scale winds diminish across the state from Sunday night through Tuesday, local scale land and sea breezes will develop. Windward cloud and shower activity will shift towards mountain and island interior areas with clearing trends at night. Any showers that develop will favor these interior sections in the afternoon to early evening hours as heating declines and clouds build ups start to collapse.
A second low pressure system will move into the region from the northwest with a cold front, reinforcing the trough stalling out just west of Kauai from Tuesday to Wednesday. The western islands of Kauai and Oahu will see a shift in wind directions from land and sea breezes to southerly wind flow. Southerly winds will last into Thursday over the western half of the state bringing up deeper tropical moisture and clouds into Kauai and Oahu. Expect increasing shower trends over both islands during this time period. The central and eastern islands in Maui and Hawaii Counties will continue to see more of a land and sea breeze weather regime during this period as the weakening front stalls near Kauai. The high pressure ridge far northeast of the islands will build back in over the Hawaii region from Friday onward with more stable easterly trade winds moving into the eastern half of the state by Friday morning.
Global weather model rainfall solutions differ on how much rainfall will develop over the western islands during this southerly wind pattern. However Kauai and Niihau are closer to the more unstable tropical moisture plume and will likely see higher rainfall totals as compared to the rest of the state. Oahu may also see a smaller increase in shower activity during the Tuesday to Thursday time period. Stay tuned for weather updates for this time period as these weather impacts will depend heavily on the final position of the approaching trough.

Aviation

Locally breezy easterly trade winds will remain in place today across the island chain with surface high pressure located far northeast of the state. However, this high will weaken slightly throughout the weekend and trade winds speeds should gradually weaken to moderate speeds by Sunday before a land/sea breeze regime takes over early next week. Meanwhile, a sharp trade wind inversion and fairly limited moisture will limit shower coverage and intensity this weekend. Showers and low clouds that do develop will favor north through east facing sections of the islands. VFR conditions will prevail at most locations, though brief MVFR ceilings will be possible in any showers, especially during the overnight and early morning hours.
AIRMET Tango remains in effect today from Molokai to the Big Island for moderate low-level turbulence over and immediately downwind of the terrain. However, as surface wind speeds gradually weaken during the second half of the weekend, this AIRMET may be cancelled.

Marine

Fresh to strong easterly trade winds will continue through tonight, then trend down and shift out of the south to southeast late Sunday through the first half of next week as a front sets up west of the state. This will allow a land and sea breeze pattern to become established for most areas by Monday near the coasts. The southerlies may reach moderate levels by midweek over the western end of the state.
Surf along east facing shores will remain rough through tonight, then ease by early next week as the winds ease and shift out of the south to southeast. Residual background easterly trade wind swell from the upstream trades, however, will support small surf continuing into next week.
Surf along all other shores will remain small through the weekend with mainly background southerly energy moving through (another pulse expected to arrive tonight into Sunday). Surf along south facing shores will trend up Tuesday through midweek as a new, long-period south swell arrives and the local winds shift onshore due to the south winds expected (strongest Kauai by Wednesday).
Although confidence remains low due to significant model differences, a medium-period northwest swell from low pressure setting up around 1400 NM northwest of the state early next week can't be ruled out to arrive locally late next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov