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Tropical Storm NORA Forecast Discussion

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WTPZ43 KNHC 110240

800 PM PDT SAT OCT 10 2015

Nora's satellite presentation continues to feature an irregular CDO
with little in the way of convective banding. The initial intensity
remains 45 kt based on a blend of the latest TAFB and SAB Dvorak
classifications. ASCAT data received around the time of the last
advisory suggested that Nora is a very small tropical cyclone, with
tropical storm force winds only extending outward up to 30 n mi in
the northern semicircle. An AMSR2 microwave image from the JAXA
GCOM-W2 satellite around 22Z clearly showed the low-level center on
the southeastern edge of the deep convection, but convection has
formed closer to the center since that time.

The near-storm environment should be favorable for some
strengthening in the next 48 hours or so, with warm waters and low
vertical shear, but there is some mid-tropospheric dry air in the
environment that could limit strengthening. After that time, the
vertical shear begins to increase as the cyclone recurves, and
steady weakening is forecast to begin after 72 hours. The NHC
forecast generally follows the trend of the previous one, but no
longer explicitly shows Nora reaching hurricane strength. However,
this is certainly still possible. The NHC prediction is close to the
FSU Superensemble through 36 hours and near the intensity consensus
after that time.

The ASCAT data and microwave fixes indicated that the center of
Nora was located a little southwest of the position in the previous
advisory, but the initial motion remains westward at 12 kt. The
synoptic reasoning for the track forecast has not changed, as Nora
will be steered westward at a decreasing forward speed for the next
36 to 48 hours by a weakening ridge to the north. After that time,
Nora should begin to recurve into a break in the ridge and then turn
northeastward by the end of the period under the influence of a
longwave trough over the north-central Pacific. The new NHC track
forecast has been adjusted to the south and west of the previous one
through 72 hours to account for the initial position and motion, and
is near the previous official forecast track after that time. The
NHC forecast lies between the latest ECMWF forecast and the TVCE
multi-model consensus.

With Nora moving into the central North Pacific basin, this will
be the last advisory from NHC. Future information on Nora can
be found in advisories issued by the Central Pacific Hurricane
Center beginning at 1100 PM HST (0900Z).


INIT  11/0300Z 11.7N 139.9W   45 KT  50 MPH
 12H  11/1200Z 11.8N 141.5W   50 KT  60 MPH
 24H  12/0000Z 11.9N 143.2W   55 KT  65 MPH
 36H  12/1200Z 12.0N 144.6W   60 KT  70 MPH
 48H  13/0000Z 12.2N 145.6W   60 KT  70 MPH
 72H  14/0000Z 14.0N 146.5W   55 KT  65 MPH
 96H  15/0000Z 16.0N 145.8W   45 KT  50 MPH
120H  16/0000Z 17.5N 144.5W   35 KT  40 MPH

Forecaster Brennan