Area Forecast Discussion
Issued by NWS Honolulu, HI
FXHW60 PHFO 251445
Area Forecast Discussion
National Weather Service Honolulu HI
445 AM HST MON JUL 25 2016
Tropical Depression Darby will continue to bring unsettled
weather to western portions of the state this morning as the
system tracks northwestward and away from the Aloha state.
Improving conditions are then expected to spread across the island
chain from east to west through tonight. More typical trade wind
weather will then return for the remainder of the work week as
high pressure builds well northeast of the island chain.
The 5 am HST advisory from the Central Pacific Hurricane Center
(CPHC), indicated that Darby had weakened into a Tropical
Depression, and was located around 55 miles west-northwest of
Barking Sands. Infrared satellite imagery shows mostly cloudy
skies in place across the state, with radar imagery showing
moderate to heavy showers continuing to stream northward over the
island of Oahu. Main short term concern for today revolves around
the potential for heavy rainfall and flash flooding.
The latest track from CPHC continues to show Darby tracking
northwestward and away from the island chain. Deep southerly flow
on the eastern side of the weakening system will continue to
transport tropical moisture with precipitable water values in
excess of 2.0 inches across Oahu and Kauai this morning before a
slightly drier and more stable airmass moves in this afternoon. As
a result, we will continue the Flash Flood Watch for Oahu, Kauai
and Niihau through noon. Across Maui county and the Big Island,
rainfall coverage is not expected to be as great, with mainly
diurnally driven convection expected. Overall, the worst weather
associated with Darby has already occurred, with steadily
improving conditions expected through the day.
Tonight through Friday night...
More typical trade wind weather will settle over the
island chain as Darby or its remnants continue to track
northwestward and away from the Aloha state. The muggy conditions
will take some time to depart in the wake of Darby, but we should
see a noticeable decrease in humidity for the middle to latter
part of the work week. Overall, clouds and showers are expected to
focus primarily over windward and mauka locales through the
Model guidance is in good agreement showing the trade wind flow
moistening up in response to a lowering of upper level heights
over the state. There is also some indication that moisture
associated with the remnants of what is now Hurricane Georgette in
the eastern Pacific, will get caught up in the trade wind flow. As
a result, there should be an increase in trade wind showers
across the state, with the majority of the activity impacting
windward and mauka locales.
AIRMET Sierra is in effect for mountain obscurations
for Kauai, Oahu and portions of Maui County due to showers and
isolated thunderstorms on the southern end of Tropical Depression
Darby. This AIRMET is likely to remain this morning, possibly
later, until most of the showers and thunderstorms follow Darby to
the northwest. Expect improving visibility and ceilings east to
west over the next 24 hours as trade winds build in.
AIRMET Tango and Zulu is in effect for tempo moderate turbulence
and icing across Kauai and Oahu.
More significant thunderstorm coverage persists north of Kauai and
Oahu. A SIGMET is in effect for embedded thunderstorms.
All Tropical Storm Warnings have been cancelled as the latest
advisory from the CPHC indicates that Darby has weakened into a
Tropical Depression. Winds are expected to remain below headline
thresholds today as Darby tracks northwestward and further away
from the island chain. High pressure will build northeast of the
state tonight and through much of the work week, increasing the
trade wind flow across the marine area. Small Craft Advisories
(SCAs) may become necessary as early as tonight for the Alenuihaha
Channel. The SCA conditions will then likely expand to additional
marine zones through the week as the trade winds strengthen.
Surf heights are expected to remain below advisory levels through
the work week.
Flash Flood Watch until noon HST today for Niihau-Kauai-Oahu.