textproduct: Honolulu

SYNOPSIS

Locally breezy trade winds will continue for the next couple of days. After a brief lull in trades mid-week, they are expected to strengthen again during the latter portion of the week. Another round of moisture will move in from the east by mid-week as well. This will increase chances for showers, including some heavier showers and isolated thunderstorms.

DISCUSSION

Early this morning, local radar imagery shows relatively few light showers across the region embedded within locally breezy trade winds. This is supported by the surface observations across the islands, which show very light rainfall accumulation has occurred overnight. The spots which did see a few light showers were primarily windward and mountain locations. Water vapor imagery shows a trough aloft in the vicinity of the western islands. Southerly flow aloft associated with this upper trough is helping draw high clouds northward over the state.

The upper trough is expected to linger near the islands for the next few days, first remaining nearly stationary near the western end of the state, then lifting slowly northward. Meanwhile, breezy trade wind flow is prevailing across the islands, which will focus the bulk of shower activity over windward and mauka locations for the next couple of days. By mid-week, the trough could disrupt surface flow enough to cause a brief dip in wind speeds across the islands. Throughout the next few days, dewpoints in the low 70s will continue the humid/muggy conditions.

Currently, the remnants of former Tropical Depression 15E remain well southeast of the islands, and recent satellite trends show that very little convection is associated with the system at this time. As that system moves to the west, a trough associated with it will bring moisture towards the islands, which will increase shower activity mid- to late week. That trough will also help to disrupt the trade wind flow. As the previous discussion mentioned, global models suggest that unstable air associated with the trough should approach the Big Island by sometime early Wednesday. With precipitable water vales reaching over 2 inches, and with this surface feature nearby to provide sufficient lift, heavier showers are likely. Isolated thunderstorms were added to the forecast over primarily the eastern end of the state with this morning's forecast package. By the end of the week, strong trades should build back into the region, and this was also reflected in this morning's forecast updates.

It remains notable that the forecast will be dependent on how global guidance handles the remnants of Tropical Depression 15E. According to the latest forecast from the National Hurricane Center, environmental conditions are conducive for some development by the middle to latter portions of the week as it moves westward to west-southwestward, south of the Hawaiian Islands. Interests should continue to monitor the status of tropical cyclone development via hurricanes.gov and local weather forecasts at weather.gov/hfo.

AVIATION

Moderate to breezy trades will continue for the next couple of days. Embedded showers will primarily impact windward and mountain areas. Kona slopes of the Big Island could also see some afternoon showers today. Brief and isolated MVFR conditions are possible within showers, but VFR should prevail.

AIRMET Tango remains in effect for moderate low-level turbulence downwind of island terrain due to the breezy trade winds.

MARINE

The gradient between weak high pressure north of the islands and pressure falls south of the islands is resulting in locally breezy trade winds across the region, confirmed by a late evening advanced scatterometer pass over the area. Therefore, a Small Craft Advisory remains in effect through Monday afternoon for the typical windy channels and waters of Maui County and the Big Island. After a brief lull in trades, they will restrengthen again during the latter portion of the week as a trough or potential weak tropical disturbance moves south of the islands. Shower coverage will also increase, along with isolated thunderstorm potential, particularly across the eastern waters.

Surf along south facing shores will remain above average through early this week as a long period SSW swell holds relatively steady for the next couple of days. This swell will then fade during the middle of the week, but will be followed by another small southerly swell shortly thereafter. West facing shores will experience a bit of the southerly wrap.

Breezy trade winds will maintain moderate surf along east facing shores for the next several days. Surf along north facing shores will remain flat to tiny through Monday, but could see a bump Tuesday into Wednesday. A small, long period west northwest swell will then build later in the week, increasing surf along north and west facing shores a bit more Friday into next weekend.

FIRE WEATHER

Fire weather risk remains low. Locally breezy trade winds are expected through at least Monday. However, dewpoints in the low 70s will keep relative humidity in check. Inversion heights are around 6000 feet.

HFO WATCHES/WARNINGS/ADVISORIES

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