textproduct: Honolulu

SYNOPSIS

Trade winds will continue to strengthen today as Tropical Storm Moke moves generally from east to west, south of the islands. This system will deliver periods of rainfall to all islands from late tonight through Monday, with the heaviest rainfall forecast along windward and southeast slopes of the Big Island. A Flood Watch remains in effect for the Big Island. A Wind Advisory has been issued for parts of the Big Island and Maui County. Drier trade wind weather will return Tuesday.

SHORT TERM UPDATE

No changes have been made to the forecast track for Moke this morning. We still expect the possibility of flooding rains for parts of the Big Island. A Wind Advisory will go into effect at noon today for parts of the Big Island and Maui County. Skies were clear to partly cloudy for most areas this morning (Oahu was the exception with mostly cloudy skies), and light trade showers were moving into windward Big Island. The significant rain threat, and hence the Flash Flood Watch, is not expected to begin until midnight tonight. No changes will be made to the forecast at this time.

PREV DISCUSSION

Issued at 357 AM HST Sat Aug 22 2026 Latest IR satellite imagery loop continues to show deep convection several hundred miles southeast of the Big Island, in association with Tropical Storm Moke. The center of Tropical Storm Moke was located roughly 500 miles southeast of Hilo and moving at around 12 mph to the west northwest. Closer to home, mainly clear skies prevail with few low clouds pushing against the island's windward slopes. The 06Z Hilo sounding shows a fairly shallow subsidence inversion height near 5000 feet with relatively dry air both above and below the inversion. Thus, it comes as no surprise that the radar has been quiet with only isolated light showers dotted over the region. Trade winds have begun to slowly ramp up statewide the last several hours into a more moderate range, generally 10 to 20 mph, with gusts to around 30 mph at wind prone sites.

Local pressure gradients will further tighten today as Hawaii becomes sandwiched between the low pressure of Tropical Storm Moke (as it moves west, south of the islands) and a 1026 mb surface high far to the northeast of the region. Winds across select zones of Maui County and the Big Island, mainly the typical tradewind prone zones in the lee of mountains or passes, should reach advisory level by this afternoon. A Wind Advisory has been issued for these areas and has a starting time of noon. Hi-resolution model guidance indicates nearing High Wind Warning levels in the lee of the Kohala mountains on Big Island later this evening into tonight. If this comes to fruition, and winds increase above guidance, the advisory for this zone would need to be upgraded. Leeward Ko'olau mountains and Wai'anae mountain zones on Oahu may be added to the advisory on a later shift as winds near criteria this evening into tonight. Trade winds remain strong through Sunday, then begin to dwindle late Sunday into Monday morning.

By this evening, a slug of deeper low level moisture from Tropical Storm Moke begins to approach the Big Island from the east. Showers will become numerous along windward and southeastern sections of the Big Island late tonight through Monday with periods of embedded heavy rain. Both the GFS and ECMWF share similar solutions and the NHC track forecast for Moke has changed very little during the past several advisories. For this reason, forecast rain amounts were held steady overnight with no major changes. A Flood Watch for the Big Island will go into effect tonight and continue through Monday afternoon. Rainfall totals of 5 to 10 inches, locally up to 15 inches are possible over the windward and southeast slopes of the Big Island. It will not take a significant amount of rain to cause flash flooding due to saturated grounds from recent heavy rain. For the remaining islands, showers will also become more numerous as deeper low level moisture increases from Tropical Storm Moke. However, totals should be much less with only up to a few inches of rainfall accumulation expected. Isolated amounts up to 4 inches are possible over the eastern portion of Maui as moist easterly flow moves up the slope of Haleakala.

Early next week, as Tropical Storm Moke pushes further west, away from the islands, both the GFS and ECMWF indicate some residual moisture and instability left behind in its wake. This could spell more weather weather for the area, especially over the higher terrain of Maui and the Big Island. Details will be worked out in the coming days. By Wednesday, a surface high northeast will once again dominate and bring a return of more typical trade wind weather.

AVIATION

Trade winds will fill back in over the islands as Tropical Storm Moke approaches and passes south of the Big Island this weekend, increasing the pressure gradient across the state. Trades will gradually strengthening from east to west, becoming strong by this afternoon and continuing to build on Sunday.

AIRMET Tango is in effect starting 21Z for low level turbulence downwind of island terrain.

While occasional pockets of MVFR conditions will be possible within passing showers along windward and mauka locations today, VFR conditions are expected to prevail. Tonight into Sunday, increasing moisture over the eastern end of the state as Tropical Storm Moke passes by to our south will result in increasing chances for heavy rainfall, along with low visibilities and ceilings, across the Big Island. This will bring more widespread MVFR and IFR conditions.

MARINE

Trades are strengthening in response to Tropical Storm Moke approaching from the south and the Small Craft Advisory for winds and seas remains in effect through the weekend. Breezy trades then persist well into next week.

Surf along E and SE shores gradually builds this weekend in response to strengthening trades and short period fresh swell emanating from Tropical Storm Moke. The direction of this swell will transition to S and then SW as Moke advances west. A High Surf Advisory (HSA) may be needed for the SE shores of the Big Island tonight into Sunday, but at this time it appears surf will fall shy of the HSA threshold.

Surf along S shores remains slightly below the summer average but still slightly elevated through the weekend due to a small, long period SW swell. A series of long period S swells arrive during the middle of next week potentially bumping surf to the advisory threshold.

A small medium to long period NW swell originating from Hurricane Lala provides elevated surf along N and W shores this weekend.

FIRE WEATHER

Issued at 357 AM HST Sat Aug 22 2026 Trade winds continue to increase today and the inversion, currently around 5-6 kft, will steadily weaken and eventually erode altogether as deep moisture associated with TS Moke moves into the area tonight into Sunday. Heavy rain is expected over windward and SE facing slopes of the Big Island on Sunday.

HFO WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 6 PM HST Sunday for Big Island Interior-Big Island North-Big Island South-Big Island Southeast-Kahoolawe- Kohala-Lanai Leeward-Lanai Mauka-Lanai Windward-Maui Central Valley North-Maui Central Valley South-Maui Leeward West-Molokai Leeward South-Molokai North-Molokai Southeast-Molokai West-South Haleakala-Windward Haleakala.

Flood Watch from late tonight through Monday afternoon for Big Island East-Big Island Interior-Big Island North-Big Island South-Big Island Southeast-Big Island Summits-Kohala-Kona.

Small Craft Advisory from 6 PM this evening to 6 PM HST Sunday for Kauai Channel-Kauai Leeward Waters-Kauai Northwest Waters- Kauai Windward Waters.

Small Craft Advisory until 6 PM HST Sunday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Big Island Windward Waters-Kaiwi Channel-Maalaea Bay-Maui County Leeward Waters-Maui County Windward Waters-Oahu Leeward Waters- Oahu Windward Waters-Pailolo Channel.