West Side

Today: Mostly sunny with isolated showers. Highs 77 to 89. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows 68 to 77. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Sunny. Highs 79 to 90. East winds up to 15 mph.

South Side

Today: Sunny. Highs 79 to 91. North winds up to 10 mph.

Tonight: Mostly clear. Lows 70 to 75. North winds up to 15 mph.

Tuesday: Sunny. Highs 80 to 91. North winds 10 to 15 mph.

North Shore

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 88 near the shore to around 71 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 73 near the shore to around 57 near 5000 feet. Southeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 89 near the shore to around 71 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Central Maui

Today: Sunny. Highs 84 to 91. Northeast winds up to 15 mph.

Tonight: Mostly clear. Lows around 72. Northeast winds up to 15 mph.

Tuesday: Sunny. Highs 84 to 91. Northeast winds 10 to 15 mph.

Upcountry

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 54 to 72. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 51 at the visitor center to around 45 at the summit. East winds up to 15 mph increasing to 10 to 15 mph after midnight.

Tuesday: Sunny and breezy. Highs 56 to 74. East winds 10 to 20 mph.

East Maui

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 88 near the shore to around 71 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 73 near the shore to around 57 near 5000 feet. Southeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 89 near the shore to around 71 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Lanai City

Today: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs 72 to 83. North winds up to 15 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Isolated showers. Lows 63 to 70. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 73 to 83. Light winds. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny with isolated showers. Highs 75 to 91. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows 61 to 76. East winds 10 to 15 mph.

Tuesday: Mostly sunny. Breezy. Highs 75 to 91. East winds 10 to 20 mph.

Detailed Forecast

Synopsis

Light to moderate trades and sea breezes over leeward areas will continue today as a low level trough drifts westward through the island chain. Higher humidity levels will also continue along with increasing showers over the central and western islands. The weather pattern changes on Tuesday as the ridge builds back into the region and locally breezy trade winds return with stable and rather dry conditions statewide lasting into next weekend.

Discussion

The satellite imagery this morning shows bands of clouds associated with a weak low level trough drifting westward through the islands. Lighter trade wind speeds, higher humidity levels and increasing shower trends will continue today due to this passing disturbance over central and western islands. Shower activity this morning will continue to favor windward and mountain areas with a few of the stronger showers drifting into typically drier leeward areas. Lighter large scale winds today will continue to allow daytime local scale sea breezes to expand over most islands. Interior clouds building in over leeward mountain slopes may produce a few afternoon showers, especially along the Kona slopes of the Big Island.
Expect drier and more stable conditions to move into the islands from Tuesday onward as the trough departs the pattern to the west and the subtropical ridge builds back in over the region. Trade winds will increase into the moderate to locally breezy range in a noticeably drier and more stable environment.
Tropical cyclone activity continues to heat up far southeast of the Hawaiian Islands as Tropical Storm Iona, along with a second developing tropical disturbance potentially deepening just to the east of Iona. The track of both systems based on National Hurricane Center advisories for Iona and global forecast models for the tropical disturbance will likely continue to drift in a general westward direction; passing far south of the Hawaiian Islands. Trade wind speeds may increase slightly as compared to our current forecast as these tropical systems pass far south of the islands, lowering subsidence temperature inversion heights, and limiting clouds and showers from Wednesday through Friday.

Aviation

Light to moderate large scale trade winds today will allow local scale daytime sea breezes to expand in coverage across most islands. Clouds and showers will be enhanced over the central and western islands today with brief MVFR conditions through the early morning hours favoring N thru E slopes of island mountains. Drier and more stable conditions return with increasing trade winds from Tuesday onward as the ridge builds back into the region.
AIRMET Sierra remains in effect for Mountain Obscurations along N thru E slopes of Kauai, Oahu, Molokai, Maui and the Big Island. These conditions will likely diminish in coverage later this morning for all islands except possibly for the island of Kauai, where low clouds may linger into the afternoon hours.

Marine

A weak trough moving through the area will drift westward and weaken today as high pressure far northwest of the state gradually strengthens throughout the week. Trade winds will be gentle to locally fresh through the day then strengthen tonight into Wednesday to moderate to locally strong levels. As the trades strengthen, a Small Craft Advisory for the windier waters and channels around Maui County and the Big Island is in place for tonight. Trade winds are expected to strengthen further by Tuesday and remain strong through the week, which will cause the expansion of the Small Craft Advisory to other coastal water zones.
Tropical Storm Iona located far southeast of the Big Island is expected to pass far south of the state as a Hurricane around the middle of the week. Minimal impacts are expected, but some moderate south swells will be possible. Over the offshore waters, Tropical Storm Iona could bring some isolated thunderstorms for the far southern areas of the offshore waters. Additional tropical cyclone formation is possible within 48 hours and could impact the far south offshore waters this week. For more info, please check the public advisories on Tropical Storm Iona under WMO header WTPA31 PHFO and under AWIPS header HFOTCPCP1. Forecast/Advisories on Tropical Storm Iona are issued under WMO header WTPA21 PHFO and under AWIPS header HFOTCMCP1.
South facing shores will remain small today with mainly background energy. A storm force low east of New Zealand last week Wednesday (7/23) will send a moderate long-period south swell, which should be filling in as early as Tuesday. This initial south swell should peak on Wednesday near or slightly above the summer average. A much stronger hurricane force low developed southeast of New Zealand on Thursday (7/24) and tracked northward while gradually weakening. This low should send a long-lived south swell with forerunners arriving as early as Wednesday and steadily building through Thursday. This swell will likely peak late Thursday into Friday at High Surf Advisory thresholds and gradually fade over the weekend into early next week.
East facing shores will remain small through today before slowly rising Tuesday through the rest of the week as trade winds increase. Southeast swell from Tropical Storm Iona will also be possible during the second half of the week. Flat summer time surf will continue along north facing shores this week. An out of season small long-period northwest swell will be possible late this weekend from Typhoon Krosa currently located in the western Pacific.

Fire weather

Expect higher humidity levels in a hybrid trade wind and sea breeze pattern today, as a low level disturbance moves westward through the islands mitigating fire weather concerns. Drier and more stable conditions return as the high pressure ridge builds back in from Tuesday onward. A few leeward areas of Maui and the Big Island may briefly reach fire weather minimum humidity thresholds for a few hours each afternoon, however the sustained wind speeds are forecast to remain just below critical thresholds.
Tropical cyclone activity developing far south to southeast of the Hawaiian Islands will continue to add some uncertainty to the wind speed forecast this week, and will keep near critical fire weather conditions possible for Maui and the Big Island lasting into the weekend.

HFO Watches/Warnings/Advisories

Small Craft Advisory from 6 PM this evening to 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory from 6 AM Tuesday to 6 PM HST Tuesday for Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.

Data Courtesy of NOAA.gov