Hurricane Fernanda Discussion Number 18
NWS National Hurricane Center Miami FL EP062017
200 AM PDT Sun Jul 16 2017
A 0235Z SSMI/S microwave overpass indicated that Fernanda was still
undergoing an eyewall replacement cycle (ERC), with concentric
eyewalls remaining at about 20 and 45 n mi diameters. Although the
eye has once again cleared out and become warmer, the convective
cloud tops surrounding the eye have not cooled much. However, the
overall convective cloud pattern has improved and become more
symmetric, and outer banding features have developed in the
southeastern semicircle. Satellite intensity estimates are a
consensus T6.0/115 kt from TAFB and SAB, and T6.2/122 kt from
UW-CIMSS ADT. Therefore, the intensity has been increased slightly
to 115 kt, making Fernanda once again a category 4 hurricane.
The initial motion estimate is 285/10 kt. There is no significant
change to the previous track forecast reasonings. Fernanda is
forecast to be steered generally west-northwestward for the next 72
h by a large low-/mid-level ridge that spans the central and eastern
Pacific Ocean, extending from north of the Hawaiian Islands eastward
to the U.S. west coast. After that time, a broad upper-level trough
currently located north of Hawaii is expected to weaken and lift
out to the northeast, causing the ridge to build slightly southward
and forcing Fernanda on a more westward track. The new NHC track
forecast is similar to the previous advisory track, and lies close
to the consensus model TVCN.
Although Fernanda has about 24 hours or so remaining over warm-water
and within a low vertical wind shear environment, there are already
indications in SST data from Remote Sensing Systems that upwelling
beneath the hurricane has begun. This cooler water, coupled with the
ongoing ERC, makes the intensity forecast difficult in the near
term. As a result, little change from the current intensity is
forecast for the next 24 hours, although some intensity fluctuations
could easily occur during that time. By 36 hours and beyond, steady
weakening is forecast as Fernanda moves over sub-26C SSTs, and
enters a hostile westerly wind shear regime by 96-120 hours. The
official intensity forecast is similar to the previous one, and
closely follows the consensus models ICON and IVCN.
FORECAST POSITIONS AND MAX WINDS
INIT 16/0900Z 12.1N 126.2W 115 KT 130 MPH
12H 16/1800Z 12.6N 127.9W 115 KT 130 MPH
24H 17/0600Z 13.4N 130.1W 115 KT 130 MPH
36H 17/1800Z 14.2N 132.0W 105 KT 120 MPH
48H 18/0600Z 15.1N 133.5W 95 KT 110 MPH
72H 19/0600Z 16.6N 136.2W 70 KT 80 MPH
96H 20/0600Z 17.3N 139.4W 50 KT 60 MPH
120H 21/0600Z 17.6N 142.7W 35 KT 40 MPH
$$
Forecaster Stewart
NWS National Hurricane Center Miami FL EP062017
200 AM PDT Sun Jul 16 2017
A 0235Z SSMI/S microwave overpass indicated that Fernanda was still
undergoing an eyewall replacement cycle (ERC), with concentric
eyewalls remaining at about 20 and 45 n mi diameters. Although the
eye has once again cleared out and become warmer, the convective
cloud tops surrounding the eye have not cooled much. However, the
overall convective cloud pattern has improved and become more
symmetric, and outer banding features have developed in the
southeastern semicircle. Satellite intensity estimates are a
consensus T6.0/115 kt from TAFB and SAB, and T6.2/122 kt from
UW-CIMSS ADT. Therefore, the intensity has been increased slightly
to 115 kt, making Fernanda once again a category 4 hurricane.
The initial motion estimate is 285/10 kt. There is no significant
change to the previous track forecast reasonings. Fernanda is
forecast to be steered generally west-northwestward for the next 72
h by a large low-/mid-level ridge that spans the central and eastern
Pacific Ocean, extending from north of the Hawaiian Islands eastward
to the U.S. west coast. After that time, a broad upper-level trough
currently located north of Hawaii is expected to weaken and lift
out to the northeast, causing the ridge to build slightly southward
and forcing Fernanda on a more westward track. The new NHC track
forecast is similar to the previous advisory track, and lies close
to the consensus model TVCN.
Although Fernanda has about 24 hours or so remaining over warm-water
and within a low vertical wind shear environment, there are already
indications in SST data from Remote Sensing Systems that upwelling
beneath the hurricane has begun. This cooler water, coupled with the
ongoing ERC, makes the intensity forecast difficult in the near
term. As a result, little change from the current intensity is
forecast for the next 24 hours, although some intensity fluctuations
could easily occur during that time. By 36 hours and beyond, steady
weakening is forecast as Fernanda moves over sub-26C SSTs, and
enters a hostile westerly wind shear regime by 96-120 hours. The
official intensity forecast is similar to the previous one, and
closely follows the consensus models ICON and IVCN.
FORECAST POSITIONS AND MAX WINDS
INIT 16/0900Z 12.1N 126.2W 115 KT 130 MPH
12H 16/1800Z 12.6N 127.9W 115 KT 130 MPH
24H 17/0600Z 13.4N 130.1W 115 KT 130 MPH
36H 17/1800Z 14.2N 132.0W 105 KT 120 MPH
48H 18/0600Z 15.1N 133.5W 95 KT 110 MPH
72H 19/0600Z 16.6N 136.2W 70 KT 80 MPH
96H 20/0600Z 17.3N 139.4W 50 KT 60 MPH
120H 21/0600Z 17.6N 142.7W 35 KT 40 MPH
$$
Forecaster Stewart
