Maunakea Weather Center

NWS Bulletins for NPAC - MKWC

Menu of Text Products for the Hawaiian Islands and the Tropical Pacific/Atlantic Oceans:
Narrow the Menu List
Select Time Limit: 12 hours | 24 hours | 48 hours | 72 hours | No time limit
Select Product Type: All | Routine Bulletins/FCSTS | Warnings/Watches/Advisories | HAWN Weather | Tropical | Marine | Aviation | Daily Obs | Special

Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 301321

Area Forecast Discussion
National Weather Service Honolulu HI
321 AM HST Tue May 30 2023

Moderate trades will focus showers over windward areas through
the week. Afternoon showers, some of which may be heavy, will be
common over leeward portions of Maui and the Big Island each
afternoon. There is also a slight chance of afternoon
thunderstorms over the Big Island today.


Did make some tweaks to the PoPs and associated grids through
tomorrow night, mainly to nudge PoPs up towards the National Blend
of Models. This mostly impacted the Big Island, but some other
areas were nudged upwards as well. The overall forecast philosophy
remains the same.

An upper level trough to the north of the main Hawaiian islands is
bringing southwesterly upper level winds over the region. High
clouds just south of the Big Island will likely pass over the
island from time to time. Thunderstorms have been noted on the
edge of the coastal waters to the southwest of the islands, and
into the offshore waters further southwest.

The upper level trough is expected to slowly lift north and move
to the east over the next 24 hours or so. While thunderstorms
didn't materialize over the Big Island yesterday afternoon,
enough instability remains over the southern end of the state for
the possibility of a thunderstorm or two over the slopes Tuesday

The surface trough mentioned above is expected to move to the west
away from the islands over the next couple of days, with a high
pressure system remaining to the north to maintain a trade wind
pattern over the islands. A broad upper level trough is expected
to remain north of the islands through much of the week. The ECMWF
develops another upper level low to the northwest of the islands
at the end of the week, while the GFS isn't quite as keen on the
development. The upper level trough will likely keep inversion
levels a bit higher than normal in a trade wind pattern. With
precipitable water on the high end of normal, there will be
showers focused over the windward sides of the islands. The higher
than normal inversion will help showers to develop over the
leeward sides of the islands during the afternoon hours,
particularly Maui and the Big Island, through the week.



The air mass over the state is becoming increasingly unstable,
the result of a nearby upper level trough of low pressure. With
little or no capping inversion aloft, locally heavy showers are
possible statewide. Daytime heating will further enhance
convective activity, especially over island interiors. Isolated
thunderstorms are expected over the higher elevations of the Big
Island in the afternoon and early evening.

Early morning satellite and radar imagery revealed scattered
light showers carried in by the trade winds approaching windward
slopes and coasts. Meanwhile, a large area of layered clouds,
punctuated with isolated moderate showers, hung over leeward
waters. In the higher levels, ragged bands of cirrus streamed across
the state from the southwest. Expect shower activity to be mainly
light and intermittent this morning then intensify and become
focused over island interiors in the afternoon.

There are currently no AIRMETs in effect.


High pressure far north of the state will drift south for the next
couple of days. This will result in moderate to fresh trade winds
with periods of locally strong trade winds. Winds will hover near
the Small Craft Advisory (SCA) thresholds for the windier waters
around Maui and the Big Island and could increase to SCA
thresholds briefly Wednesday. Trades winds will weaken slightly as
the high moves far northeast towards the end of the week into the

The current south southwest swell appears to have peaked and is
expected to hold surf heights around the summer average (5 feet)
today before gradually subsiding Wednesday. Background surf is
expected along south facing shores from Thursday into Friday which
will keep surf from going flat. A small, long- period south-
southwest swell will arrive this weekend providing a slight
increase in surf heights along south facing shores Saturday night
into Sunday. A small south- southeast (160-170 degree) swell is
possible early next week from a gale low located currently near

Persistent trade winds, should keep near to just below average
choppy surf along east facing shores through most of the week.
Surf is expected to drop well below average over the weekend as
trade winds ease locally and upstream.

The current small west-northwest swell will provide a slight
boost in surf heights along most exposed north and west facing
shores today. This swell will fade overnight into tomorrow. Expect
small, background summertime surf along north facing shores from
tomorrow through next weekend. For the long-range, the latest
guidance from the WAVEWATCH III Model continues to indicate a
small, long- period west swell, produced by northwest Pacific
Typhoon Mawar, may arrive around Tuesday, June 6.






Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office