957
WTPZ45 KNHC 291434
TCDEP5
Tropical Storm Miriam Discussion Number 14
NWS National Hurricane Center Miami FL EP152018
800 AM PDT Wed Aug 29 2018
Although Miriam remains a sheared tropical cyclone, recent
geostationary satellite data and a 1002 UTC AMSR2 microwave
overpass indicates that there has been some improvement in the
structure of the cyclone. The microwave data showed an increase in
banding over the eastern portion of the circulation and less
separation between the convection and the low-level center.
Therefore, the initial intensity is increased to 60 kt, which is a
blend of the most recent subjective Dvorak classifications and
objective T-numbers from UW/CIMSS. The northwesterly shear over
the cyclone appears to have abated slightly, and a further slight
reduction in shear could allow Miriam to reach hurricane strength
within the next 24-36 h. Most of the intensity guidance agrees,
and the NHC intensity forecast has been increased slightly for the
first 36 h. After that time, increasing shear and cooler waters are
expected to cause Miriam to weaken fairly quickly and the system is
forecast to become a remnant low by day 4.
Miriam continues to move westward or 275/10 kt. The cyclone is
approaching the western edge of the subtropical ridge, and the
global models indicate that Miriam will slow down and turn
west-northwestward very soon. By Thursday, a large mid- to
upper-level trough to the northeast of the Hawaiian Islands is
expected to cause Miriam to turn northwestward, then northward
through 72 hours. At days 3 and beyond, there continues to be
significant model differences with the ECMWF still taking Miriam
faster and much farther northward, while the GFS moves a much
weaker Miriam westward. Since Miriam is forecast to weaken and
become a shallow system around that time, the NHC forecast leans
toward the more westward scenario, but is not as far south and west
as the GFS. The new NHC track is south of the various consensus aids
at day 5, and is in best agreement with the GFS ensemble mean
and UKMET model.
FORECAST POSITIONS AND MAX WINDS
INIT 29/1500Z 14.2N 139.4W 60 KT 70 MPH
12H 30/0000Z 14.4N 140.6W 65 KT 75 MPH
24H 30/1200Z 15.1N 141.6W 65 KT 75 MPH
36H 31/0000Z 16.3N 142.0W 65 KT 75 MPH
48H 31/1200Z 17.9N 142.1W 60 KT 70 MPH
72H 01/1200Z 21.0N 142.9W 45 KT 50 MPH
96H 02/1200Z 23.8N 145.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 03/1200Z 26.7N 149.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
Forecaster Brown
154
WTPZ41 KNHC 291434
TCDEP1
Tropical Storm Norman Discussion Number 5
NWS National Hurricane Center Miami FL EP162018
800 AM PDT Wed Aug 29 2018
The cloud pattern has continued to improved in organization, and
SSMIS data at 1400 UTC indicate that an inner core is beginning to
form. The area of convection is large with a well defined
cyclonically curved band wrapping around the system, while the
upper-level outflow is expanding westward. Based on objective and
subjective T-numbers, the initial intensity has been set at 55 kt.
The environment of low shear and warm waters is ideal for Norman to
intensify, and in fact, the Rapid Intensification (RI) indices are
quite high. On this basis, the NHC forecast calls for Norman to
become a hurricane by tonight and a major hurricane in a day or so.
The best estimate of the initial motion is toward the
west-northwest or 285 degrees at 9 kt. The hurricane is ready to
start moving more westward or even on a west-southwestward track as
the nose of the ridge to the north begins to expand westward and
amplify. Most of the models captured the building of the ridge, and
unanimously forecast the cyclone to move west-southwestward for the
next 2 to 4 days. The confidence is the forecast during the first 3
to 4 days is high since track models are really clustered. The new
NHC forecast is not too different from the previous one, and it lies
between the corrected consensus HCCA and the multimodel aids.
FORECAST POSITIONS AND MAX WINDS
INIT 29/1500Z 17.8N 115.7W 55 KT 65 MPH
12H 30/0000Z 17.9N 116.6W 65 KT 75 MPH
24H 30/1200Z 18.1N 118.2W 90 KT 105 MPH
36H 31/0000Z 17.9N 119.8W 105 KT 120 MPH
48H 31/1200Z 17.5N 121.4W 110 KT 125 MPH
72H 01/1200Z 16.2N 124.8W 110 KT 125 MPH
96H 02/1200Z 16.0N 129.0W 100 KT 115 MPH
120H 03/1200Z 17.5N 134.0W 90 KT 105 MPH
$$
Forecaster Avila
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