Flash Flood Warning 15, NWS Honolulu, HI

059 
WGHW70 PHFO 300337
FFSHFO

Flash Flood Statement
National Weather Service Honolulu HI
537 PM HST TUE AUG 29 2017

HIC003-300545-
/O.CON.PHFO.FF.W.0015.000000T0000Z-170830T0545Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Honolulu HI-
537 PM HST TUE AUG 29 2017

...THE FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 745 PM HST FOR THE
ISLAND OF OAHU IN HONOLULU COUNTY...

At 534 PM HST...radar continues to show areas of heavy rain across 
the Koolau range. The heavy rain has begun to taper off in town and 
along H-1, but has started to increase over the northern half of the 
Koolau range. Drivers should continue to exercise caution on the 
roadways. 

Locations in the warning include but are not limited to...
Honolulu, Waimanalo, Haleiwa, Wahiawa, Schofield Barracks, Hawaii
Kai, Ahuimanu, Punaluu, Wheeler Field, Waikele, Kalihi and Waiahole.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A flash flood warning means that flooding is imminent or occurring in
streams, roads, and low lying areas. Move to higher ground now.

Do not cross fast flowing water in your vehicle, or on foot. Turn
around, don/t drown.

&&

This warning may need to be extended beyond 745 PM HST if heavy rain
persists.

LAT...LON 2153 15784 2147 15784 2141 15777 2145 15778
      2147 15773 2146 15773 2141 15774 2131 15765
      2126 15770 2130 15772 2126 15782 2134 15790
      2130 15791 2135 15797 2132 15799 2159 15812
      2167 15806 2171 15797

$$

M Ballard

091 
WGHW70 PHFO 300534
FFSHFO

Flash Flood Statement
National Weather Service Honolulu HI
734 PM HST TUE AUG 29 2017

HIC003-300541-
/O.CAN.PHFO.FF.W.0015.000000T0000Z-170830T0545Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Honolulu HI-
734 PM HST TUE AUG 29 2017

...THE FLASH FLOOD WARNING FOR THE ISLAND OF OAHU IN HONOLULU COUNTY
IS CANCELLED...

Weather radar showed that heavy rains have dinimished a bit. 
Localized ponding of some roads will continue.

LAT...LON 2153 15784 2147 15784 2141 15777 2145 15778
      2147 15773 2146 15773 2141 15774 2131 15765
      2126 15770 2130 15772 2126 15782 2134 15790
      2130 15791 2135 15797 2132 15799 2159 15812
      2167 15806 2171 15797

$$

Area Forecast Discussion
National Weather Service Honolulu HI
334 PM HST Tue Aug 29 2017

.SYNOPSIS...
Weak ridge north of the islands will maintain light to locally
moderate trade winds for the next couple of days with clouds and
showers favoring windward and mauka areas with some afternoon
clouds and showers possible over interior areas. Winds will become
lighter by the weekend as a front approaches the area from the
northwest. The weekend will see showers favoring interior and lee
areas during the afternoon hours, with passing showers possible
along windward areas.

&&

.DISCUSSION...
A pair of surface highs remain to the northeast and northwest of
the islands, with a surface ridge to the north. The surface
analysis this morning had a 1022 mb high about 1200 miles to the
northeast of Oahu, and a 1021 mb high about 1500 miles to the
northwest. The ridge was analyzed about 375 miles north of Oahu. A
weak surface trough remains about 350 miles to the northeast of
Oahu helping to destabilize the airmass and disrupt the trade
wind flow.

Despite the interruptions, some areas continue to experience
locally moderate trade winds, while others have been experiencing
light trade winds. Around 1 pm this afternoon, a batch of showers
began to move onshore on the east side of Oahu and have brought
briefly heavy rainfall to the Koolau range. Shortly thereafter,
showers began to form over the Waianae range, and showers off of
Molokai began to move towards Oahu. Smaller pockets of showers are
found over the remaining islands. Have boosted PoPs for some areas
of Molokai and Oahu for tonight.

An upper level low is depicted on water vapor about 500 miles to
the northeast of Oahu this afternoon. This upper level low is
forecast to remain nearly stationary for the next day or so, and
then lift northward. As the upper low lifts out, there could be a
brief time for more areas to experience moderate trade winds.

However as we head towards the holiday weekend, both the GFS and
ECMWF indicate a front approaching from the northwest. This will
weaken the winds near the islands, and then depending on the
solution, a front could reach Kauai by Sunday night. The GFS
remains the model with a more defined front and higher rainfall
totals. Have left the longer range grids as is for now, and will
continue to monitor future runs.

Dewpoints already in the 70s are expected to continue through the
holiday weekend. As the winds lighten, conditions will feel even
muggier. With light winds, and southerly winds, in the forecast,
the smaller islands can expect to see the vog from the Big Island
at times.

&&

.AVIATION...
Moisture embedded in light to locally moderate trade wind flow is
producing some MVFR conditions over windward and mauka areas.
Daytime heating has also caused for clouds and showers to form
over some interior and leeward locations where brief MVFR
conditions can be expected mainly in SHRA. Windward TAF sites will
continue to see some MVFR conditions through this evening while
most leeward TAF sites should remain VFR. AIRMET SIERRA for
mountain obscuration is posted for northeast sections of the Big
Island, Maui and Oahu. These conditions may spread to Kauai this
evening. Conditions are expected to improve overnight for most
areas.

&&

.MARINE...
Weak ridging north of the islands will maintain mainly moderate
trades through Thursday night. The ridge will shift southward over
the islands allowing winds in response to an approaching front. Winds
will weaken to light and variable Friday through the weekend.

A mix of small southeast and southwest swells will continue
through Wednesday. An above-average south swell is expected to
build beginning on Wednesday night. This swell will peak around
Friday morning and remain elevated into Saturday, and will likely
produce advisory level surf along south facing shores by Thursday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...M Ballard
AVIATION...
MARINE...