WTPA33 PHFO 212036
TCPCP3

BULLETIN
TROPICAL STORM DARBY ADVISORY NUMBER 41
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016
1100 AM HST THU JUL 21 2016

…DARBY EDGING CLOSER TO HAWAII WITH LITTLE CHANGE IN STRENGTH…

SUMMARY OF 1100 AM HST…2100 UTC…INFORMATION
———————————————–
LOCATION…18.6N 146.6W
ABOUT 560 MI…900 KM E OF HILO HAWAII
ABOUT 755 MI…1215 KM ESE OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS…65 MPH…100 KM/H
PRESENT MOVEMENT…W OR 260 DEGREES AT 14 MPH…22 KM/H
MINIMUM CENTRAL PRESSURE…998 MB…29.47 INCHES

WATCHES AND WARNINGS
——————–
CHANGES WITH THIS ADVISORY:

A Tropical Storm Watch has been issued for Hawaii County
and Maui County.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm watch is in effect for…
* Hawaii County
* Maui County

A Tropical Storm watch means that tropical storm conditions are
possible within the watch area within 48 hours.

Interests elsewhere in the Hawaiian Islands should monitor the
progress of Darby.

DISCUSSION AND 48-HOUR OUTLOOK
——————————
At 1100 AM HST (2100 UTC), the center of Tropical Storm Darby was
located near latitude 18.6 North, longitude 146.6 West. Darby is
moving toward the west near 14 mph (22 km/h). While this general
motion is expected to continue over the next 48 hours, some
decrease in forward speed is expected late Friday into Saturday.

Maximum sustained winds are near 65 mph (100 km/h) with higher
gusts. Little change in strength is forecast during the next 48
hours.

Tropical-storm-force winds extend outward up to 105 miles (165 km)
from the center.

The estimated minimum central pressure is 998 mb (29.47 inches).

HAZARDS AFFECTING LAND
———————-
WIND: Tropical-storm-force winds are possible over the Big Island
and portions of Maui county on Saturday.

SURF: Swells generated by Darby are expected to reach the Hawaiian
Islands over the next couple of days, possibly becoming damaging
along some coastlines Friday and Saturday.

RAINFALL: Heavy rains associated with Darby are expected to reach
the Big Island and portions of Maui county late Friday, potentially
impacting the remainder of the state Saturday and Sunday.

NEXT ADVISORY
————-
Next intermediate advisory at 200 PM HST.
Next complete advisory at 500 PM HST.

$$
Forecaster Birchard
WTPA43 PHFO 212106
TCDCP3

TROPICAL STORM DARBY DISCUSSION NUMBER 41
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016
1100 AM HST THU JUL 21 2016

Darby’s satellite signature has changed little since the last
advisory, with a compact area of deep convection wrapping around
the center, mainly in the northern semicircle. Although subjective
Dvorak fixes from HFO/SAB/GTW all indicated a data-T of 3.0/45 kt,
the initial intensity for this advisory will be maintained at 55 kt.
Reconnaissance aircraft from the 53rd Weather Reconnaissance
Squadron are en route to Hawaii, and initial flights into
Darby are scheduled for this time tomorrow, allowing for a much
better estimate of Darby’s actual intensity.

The initial motion for this advisory is estimated to be 260/12 kt,
with Darby being steered by a retrograding mid-level ridge centered
well north of Hawaii. This ridge will be the primary steering
mechanism over the next 48 hours or so, after which time a deep
layer low digging southward will weaken the ridge, causing a
reduction in Darby’s forward speed. Between 48 hours and 72 hours,
steering currents are expected to be weak, with Darby still expected
to make a turn toward the northwest. In the longer range, a deep
layer southerly flow should steer Darby more quickly toward the
north and lead to weakening. Latest guidance however has trended
toward a less dramatic turn, and shifted closer to Hawaii. The
updated track forecast is similar to the previous through 48 hours,
after which time it has been shifted closer to Hawaii, in response
to a significant westward shift in most of the reliable guidance,
namely the TVCN and GFEX. The official forecast lies on the right
hand side of the guidance suite, and if model trends continue, the
forecast may need to shifted westward with subsequent forecasts. The
updated track forecast necessitates the issuance of a tropical storm
watch for the Big Island and Maui County.

The intensity forecast is essentially unchanged from the previous,
with light to moderate shear inhibiting strengthening while
Darby traverses slightly warmer water over the next 48 hours.
Gradually cooling water temperatures and increasing shear are
expected to lead to a weakening trend on days 4 and 5, and the
updated forecast is close to the IVCN consensus. Of note, while the
official track forecast indicates Darby tracking over portions of
the Hawaiian Islands, the intensity forecast is thus far not
indicating significant weakening due to interaction with land.

Interests elsewhere in the Hawaiian islands should monitor the
progress of Darby, as it could eventually have impacts on all
islands. Remember, it is important not to focus too closely on the
exact track and intensity forecasts because the average track error
72 hours out is near 100 miles, while the average intensity error is
about 15 kt. In addition, the hazards of a tropical cyclone can
extend over a broad area well away from the center.

FORECAST POSITIONS AND MAX WINDS

INIT 21/2100Z 18.6N 146.6W 55 KT 65 MPH
12H 22/0600Z 18.4N 148.3W 55 KT 65 MPH
24H 22/1800Z 18.3N 150.5W 55 KT 65 MPH
36H 23/0600Z 18.5N 152.1W 55 KT 65 MPH
48H 23/1800Z 18.9N 153.6W 55 KT 65 MPH
72H 24/1800Z 20.3N 155.7W 55 KT 65 MPH
96H 25/1800Z 22.5N 157.9W 50 KT 60 MPH
120H 26/1800Z 25.5N 160.5W 40 KT 45 MPH

$$
Forecaster Birchard
H