Niu Valley, HI Weather

Synopsis

Northeasterly trade winds should gradually weaken through Monday. Brief passing showers will drift into the islands on the trade winds, favoring windward and mountain areas during the overnight to early morning hours. A significant change to our weather pattern is expected early next week. Deep tropical moisture will bring the potential for heavy rain and thunderstorms across the state starting Monday night and persisting through at least Thursday.

Short Term Update

Northeast trade winds continue this morning, with windward and mauka showers bringing light rain showers, mainly to the eastern end of the state. Showers are expected to spread to the western end of the state today, but remain on the light side. No update is needed this morning. See the previous discussion for information in our potential heavy rain coming beginning late Monday night.

Prev Discussion

Issued at 328 AM HST Sun Oct 25 2026

Radar this morning shows scattered showers along windward and mauka locations. Satellite imagery shows a large closed low about 900 miles to our northeast, a ridge to our northwest and another to our east-southeast. At the surface, a low is centered beneath the upper level low, with a ridge to either side.

Monday afternoon the low to our north will drift slowly southeast, both aloft and at the surface. At the same time, a low, CP94 and a new surface low will form to our west- southwest. A trough will connect these lows...the one that drifted into a position to our northeast along with the two to our west- southwest. Southerly winds will bring deep tropical moisture northward as this trough moves north toward and then through the state Monday night through Thursday. PWATs will get up over 2 inches, and max out around 2.5 inches.

Heavy rain and thunderstorms will be possible through this period over most of the state, but models are slow to converge on areas of maximum concern. A Hydrologic Statement describing the concern for flooding was issued yesterday afternoon. A Flood Watch may be issued if models continue to show the potential for heavy rain. Upper level winds may be just strong enough to enable the development of organized convection.

Winds will remain generally easterly through Tuesday, but after that there is uncertainty. Some models show centers of low pressure forming along the trough as it moves over the state. The location and timing of these lows depicted by various models, are quite different and therefore may result in wind variations in both speed and direction by island. This makes for a very low- confidence wind forecast. Regardless of exact timing/location of any additional lows that may form, it does not appear that strong winds will impact the state with this overall system. However, showers and any thunderstorms will have the potential for brief gusty winds.

Aviation

Moderate trade winds will prevail today with some isolated breezy conditions at PNHY and PHMK. Otherwise, windward and mountain areas on Big Island will see an increase in showers which may cause temporary MVFR ceilings and visibilities in any shower that passes through.

Moderate turbulence has been reported between 23,000 and 34,000 feet over the open water areas north and east of the islands. The moderate nature and forecast for continued weakening of the winds preclude any AIRMET or SIGMET headlines at this time.

Looking ahead, widespread MVFR/IFR conditions in heavy showers and low ceilings are possible beginning Monday Night into Tuesday morning; see the main discussion for details on the upcoming heavy rain and flooding potential.