504
FXHW60 PHFO 101330
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
330 AM HST Fri May 10 2024

.SYNOPSIS...
The threat for strong to severe thunderstorms and heavy rainfall
will continue across the state through tonight as a strong upper
level disturbance settles southward into the area. Although the
thunderstorm potential will lower early next week, plenty of
moisture lingering combined with afternoon sea breezes and a broad
surface trough nearby will support afternoon showers over
interior and leeward areas each day. The wet pattern could
continue through the latter half of next week as another upper
disturbance approaches.

&&

.DISCUSSION...
The morning water vapor imagery showed broad upper troughing over
the region with a strong shortwave trough digging southeastward
into the area. The surface trough has responded to the upper
height falls and strengthened near Kauai overnight. High-
resolution model guidance reflects this, with some depicting a
mesoscale low forming along the trough today. MUCAPES of 1000 to
2000 J/Kg combined with effective deep layer shear values of 35 to
45 knots will support a few strong to severe thunderstorms and
locally heavy rainfall that could lead to flash flooding into
Saturday.

Low-level convergent flow into this surface trough will be the
focus for heavy showers and thunderstorms through daybreak this
morning across the smaller islands, mostly impacting the nearshore
coastal waters initially. In addition to this activity over the
waters, this flow is translating to heavy showers anchoring in
some island terrain, particularly over the Koolaus and windward
areas of Oahu and on Maui near Hana. Peak rainfall totals are
closing in on 7 inches in the past 24-Hrs (as of 2 AM HST) along
the Koolaus, which has led to rapid water level rises in the
Waiahole/Waikane streams. With the next round of heavy showers
lifting northward toward these areas on Oahu, the potential for
flash flooding will be the main concern through daybreak, which
includes the peak morning commute times. A transition to more of a
widespread/statewide potential is possible today through tonight
as the upper low and surface reflection drift eastward across the
area. As a result, a Flood Watch remains in effect for the entire
state.

Guidance shows the upper low beginning to weaken as it lifts off
to the northeast later this weekend into early next week, which
will support a diminishing likelihood of thunderstorms. The
rainfall chances, however, will likely linger as the
aforementioned broad surface trough remains over or nearby to the
west Sunday through next week. Expect the light to moderate east
to southeast low-level flow to persist, which will allow the land
and sea breeze regime to hold for most areas. This combined with a
sufficient amount of moisture will keep the rainfall chances up
each day, especially through the afternoon and early evening
periods over interior/leeward areas with the sea breezes. The wet
pattern could persist through the second half of the week as
another upper low drops southward into the area drawing up deep
tropical moisture and southerly flow over the state.

&&

.AVIATION...
A broad surface trough and upper level disturbance will slowly
move south across the state today. This will bring enhanced
shower activity along with the threat of a few thunderstorms.
Thunderstorm activity will be greatest over western islands this
morning then slowly shift southeastward later today. Expect
periods of MVFR conditions as showers move through, with
occasional IFR possible under heavier showers.

AIRMET Sierra remains in effect for tempo mountain obscuration
across the smaller islands and windward sections of the Big
Island, with little change expected today.

AIRMET Tango may become necessary for moderate mid to upper level
turbulence as the upper level disturbance moves across the state.

AMD NOT SKED for PMDY continues due to equipment issues, with no
timeline for restoration.

&&

.MARINE...
An upper disturbance moving into the area from the north will
keep the threat of strong, possibly severe, thunderstorms in the
forecast through Saturday. These thunderstorms may produce
dangerous wind gusts, hail, and frequent lightning. A trough near
Kauai will strengthen and expand across the island chain today,
then linger through the weekend. As a result, light and variable
winds will replace the usual trade wind flow at the surface today
and Saturday. Light to moderate easterly trade winds will return
starting Sunday.

A long-lived south swell will affect the islands into the
weekend. Surf along south facing shores is expected to remain at
the High Surf Advisory threshold of 10 feet through this
afternoon, then gradually decline Saturday through Tuesday. A
series of overlapping long- period south swells will give another
sizable boost to south shore surf Wednesday through late next
week. This event represents the most sustained south swell of the
year.

North shore surf will remain tiny through this morning. A small
reinforcing short-period north-northwest swell will build in this
afternoon and continue through the weekend. A small long- period
northwest swell will build Sunday night, giving north shore surf a
boost early next week. Surf along east facing shores will be well
below normal levels through the middle of next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for Niihau-Kauai Leeward-Kauai
Mountains-Waianae Coast-Oahu North Shore-Olomana-Central Oahu-
Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West-Maui
Leeward West-Haleakala Summit-Kona-Kohala-Big Island Interior-
Kauai North-Kauai East-Kauai South-East Honolulu-Honolulu Metro-
Ewa Plain-Koolau Windward-Koolau Leeward-Molokai-Lanai Windward-
Lanai Leeward-Lanai South-Maui Central Valley North-Maui Central
Valley South-Windward Haleakala-Kipahulu-South Maui/Upcountry-
South Haleakala-Big Island South-Big Island Southeast-Big Island
East-Big Island North.

High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kauai
South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Leeward
South-Lanai Leeward-Lanai South-Maui Central Valley South-South
Maui/Upcountry-South Haleakala-Big Island South-Big Island
Southeast.

High Wind Warning from 6 AM this morning to 6 AM HST Saturday
for Big Island Summits.

Winter Storm Warning from noon today to 6 AM HST Saturday for
Big Island Summits.

&&

$$


DISCUSSION...Gibbs
AVIATION...Ahue
MARINE...Powell