textproduct: Honolulu

SYNOPSIS

Breezy trades will continue into Wednesday. Showers will generally favor windward and mauka areas, particularly during the overnight through early morning hours each day. Tropical Storm Lowell is about 630 miles southeast of the Big Island this evening, and is forecast to pass south of the Big Island late Wednesday into Thursday. Trade winds are expected to become strong and gusty as early as Wednesday afternoon, and continue into Friday as Lowell passes south of the state. The forecast remains uncertain for Labor Day weekend, with the potential for Lowell and Karina in the the vicinity of the state.

DISCUSSION

No changes to the forecast with the evening package, and not expecting any large scale changes with the morning package.

Clouds and showers continue to be carried in on the trade wind flow, and as a result are focused over the windward and mauka areas. A surface trough about 450 miles east of the islands will continue to move towards the islands over the next 24 hours and weaken, however moisture from that trough will reach the islands tomorrow night and be one of the reasons showers are expected to be on the increase.

Tropical Storm Lowell is about 630 miles southeast of the Big Island this evening, and the latest forecast from the National Hurricane Center (NHC) has Lowell strengthening to a hurricane overnight. The latest track and cone for Lowell has the system passing south of the islands Wednesday night through Friday. Outer rainbands and moisture from Lowell could begin to spread across the islands Tuesday, increasing chances of passing trade wind showers, however the bulk of moisture will likely pass south of the state. Additionally dewpoint temperatures are expected to exceed 70 degrees, which will make the atmosphere muggier than normal. Trade winds will stay breezy due to a strong surface high remaining far north of the area.

Overall expect an uptick in passing showers over the next few days, due to the moisture from the trough mentioned above Tuesday night, and moisture loosely associated with Lowell passing through the state.

The latest forecast from the NHC has Lowell passing a little over 300 miles south of the Big Island Wednesday night into Thursday as a category 3 Major Hurricane. While probabilities for tropical storm force winds remain low over the state, the tightening of the pressure gradient over the islands will likely produce very windy and gusty trade winds as early as Wednesday afternoon through Friday. Winds could reach advisory thresholds with wind gusts over 50 mph possible during this time.

As we head into the weekend, as Lowell exits, our focus will shift more to Hurricane Karina which is currently about 1600 miles east of the Big Island. The latest forecast from NHC for Karina brings it about 600 miles east of the Big Island on Saturday. We will continue to monitor Karina over the coming days to discern its potential impacts on the state.

The forecast spread drastically increases over the Labor Day weekend into early next week as an upper level trough/low develops north of the state. Latest 12Z run of the Google DeepMind (GDM) model continues to shows Lowell taking sharp northward turn over the weekend. While confidence has increased on Lowell passing south of the state during the week, the forecast still remains very uncertain over Labor day weekend into early next with several ensemble members of the GDM showing a sharp northward turn. Also during this time, we could see Karina within the vicinity of the islands late this weekend. Please keep an eye out on the hurricanes.gov page for the official NHC forecast for Lowell and Karina.

AVIATION

Moderate to breezy trade winds will persist through this 01/06Z - 02/06Z period. Occasional MVFR decks and brief organized showers riding within the trades will generally favor windward exposures and higher terrain. Otherwise, VFR conditions will prevail. Tropical Cyclone Lowell is forecast to pass a couple of hundred miles south of the island chain later this week. On this track, late week trade winds will strengthen as the pressure gradient tightens between Tropical Cyclone Lowell and high pressure to the far north.

AIRMET Sierra is in effect for tempo mountain obscurations for north through east sections of Kauai, Maui and Big Island due to persistent low clouds and shower coverage. AIRMET Sierra will remain in effect through tonight for these islands.

AIRMET Tango remains in effect for moderate low level turbulence south through west downstream of higher terrain. AIRMET Tango will likely be in effect for the foreseeable future.

MARINE

A strong surface high will remain nearly stationary far north of the Hawaiian Islands this week, keeping moderate to locally strong trade winds in place. Tropical Storm Lowell, now in the Central Pacific, is forecast to intensify into a hurricane tonight and will track very close to or move into the southern offshore waters, bringing possible hurricane conditions from Wednesday into Thursday. There is still some uncertainty with the forecast track of Lowell, especially closer to this weekend as the cyclone begins to gain latitude, which will have significant impacts on the wind, wave, and surf forecast for the region. Regardless of Lowell's final path, trade winds will increase by Wednesday afternoon through Friday as a result of the gradient between high pressure to the north and Lowell to the south. By this weekend, Hurricane Karina, approaching the region from the east, will increasingly be a factor in the forecast of seas and surf as well.

A small, long-period south swell will hold through tonight before a moderate south swell arrives on Tuesday. This swell will build Tuesday morning and then peak on Wednesday, bringing surf heights to just below advisory thresholds. This swell will then gradually decline through the rest of the week. Also by Wednesday, medium- period energy from Lowell could start filling in across south and southeast shores. South shore surf is likely to be elevated, but stay below advisory levels through at least Friday. Beyond that point, the surf forecast is highly dependent on the eventual track and intensity of Lowell, which has the potential to be a significant source of south to southwesterly swell through this weekend and into next week.

Trade wind swell energy will keep elevated surf heights along all east facing shores through the coming week. On Tuesday, a medium- period east swell arrives from Hurricane Karina that will build through the week and could push east shore surf to advisory thresholds by this weekend and into next week.

FIRE WEATHER

Breezy trades continuing through Tuesday, are expected to strengthen further as early as Wednesday afternoon through Friday as Tropical Storm Lowell passes south of the islands as a Hurricane. Strong gusty winds over 50 mph will be possible across select areas during this time. While fuel conditions are not at critical levels due to abundant rainfall we have received over the past several weeks, moderate fire danger will be possible for areas mainly due to very windy conditions. Dewpoints are expected to increase in the upper 60s and low 70s by Tuesday afternoon and hold through the week, keeping minimum humidities in the 50s for the most part. A few leeward areas could still see humidities down into the mid 40s especially on Thursday as a pocket of dry air moves in. The exact track of Lowell remains uncertain and thus potential for meaningful rainfall remains uncertain at this time. The inversion will hover between 5500 ft and 6500 ft the next couple of days.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Tuesday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.