[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 052032
TCDAT5

Hurricane Danielle Discussion Number  19
NWS National Hurricane Center Miami FL       AL052022
900 PM GMT Mon Sep 05 2022

After a large degradation in Danielle's appearance earlier this
afternoon, the hurricane appears to be holding more steady now with
colder cloud tops wrapping further around its center than were noted
6 hours ago. Dvorak-based intensity estimates still support an
intensity near 75 kt. The hurricane has moved a little
faster north-northeastward than anticipated during the last few
hours, with an initial motion estimate of 030/kt.

A significant adjustment was made to the track forecast at days 4
and 5, at which time Danielle is forecast to be an extratropical
cyclone. For the first 3 days of the forecast period, Danielle is
still forecast to move generally northeastward in the mid-latitude
flow. After that, it looks like Danielle could occlude and "cut-off"
from that steering flow, which may cause it to turn abruptly
northward and then southeastward at days 4-5. This scenario has been
consistently forecast for a few model cycles of the GFS and other
global models, so large changes were made to the NHC track forecast
to bring it closer to the model consensus. Other than a slight
adjustment northward and faster, no important changes were made to
the NHC track forecast for the first 72 h. Given the uncertainty at
the extended portion of the forecast, it should be noted that
confidence in the track forecast is substantially higher for the
first 72 h than the later hours. It is worth noting that Danielle
is forecast to be post-tropical by 96 h, so users should not focus
on the exact track of the cyclone since the largest impacts could
be felt far from its center.

Danielle should slowly weaken during the next few days as it moves
over marginally cool water, but most dynamical guidance suggests it
will still maintain its tropical characteristics for at least a
couple more days. Around day 3, SHIPS diagnostics indicate the
waters below the cyclone will be less than 20 deg C, and it will
likely complete its extratropical transition around that time.
The NHC forecast follows accordingly, but it should be noted this
suggests a slightly later completion to the transition than
previously forecast. The NHC intensity forecast is near the middle
of the relatively low-spread intensity guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT  05/2100Z 41.1N  43.2W   75 KT  85 MPH
 12H  06/0600Z 41.9N  42.2W   70 KT  80 MPH
 24H  06/1800Z 42.6N  40.4W   70 KT  80 MPH
 36H  07/0600Z 43.4N  38.1W   65 KT  75 MPH
 48H  07/1800Z 44.6N  35.3W   65 KT  75 MPH
 60H  08/0600Z 46.2N  32.4W   60 KT  70 MPH
 72H  08/1800Z 48.2N  29.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  09/1800Z 50.0N  29.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  10/1800Z 47.5N  25.5W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster D. Zelinsky
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