[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 060833
TCDAT5

Hurricane Danielle Discussion Number  21
NWS National Hurricane Center Miami FL       AL052022
900 AM GMT Tue Sep 06 2022

Danielle's cloud pattern has degraded further this morning by
shedding its curved bands in the eastern semicircle.  The remaining
outer bands have become more fragmented with cloud top
temperatures of only -47C.  Dvorak final-T numbers are on the
decline, and a compromise of both TAFB's and SAB's intensity
estimates, along with the UW-CIMSS objective assessment, supports
lowering the initial intensity to 65 kt for this advisory.

Although Danielle is currently moving over relatively warm (25C)
oceanic surface temperatures, the cyclone should begin to lose its
tropical characteristics soon as it traverses cooler SSTs of less
than 22C during the next day or two.  Guidance continues to
indicate that Danielle will complete its extratropical transition
on Thursday, although the vertical thermal structure shows the
system sustaining its warm core above 600 mb.  Over the
weekend, deterministic cyclone phase analyses, and simulated IR
predictions show Danielle, as the dominant system, merging with a
baroclinic system approaching from the west.  A warm seclusion
structure develops while the system occludes, or is cut-off north
of the mid-latitude westerlies.  The NHC intensity forecast is
similar to the previous advisory and continues to lean toward the
IVCN intensity consensus model.

The initial motion is estimated to be northeastward at 7 kt, and
Danielle should continue moving in this heading through this
evening.  Afterward, a turn toward the east-northeast by early
Wednesday, while accelerating, is anticipated.  By the early
weekend, the cyclone is expected to interact with a baroclinic
system by rotating cyclonically north of the westerlies and
becoming a vastly larger extratropical low well west of the British
Isles.  Once merged into one large, storm-force extratropical low,
the system should commence a general motion toward the
east-southeast on Sunday.

Danielle is producing huge seas over the central-north Atlantic.
Complete information on the High Seas Forecasts can be found at the
Ocean Prediction Center under AWIPS header NFDHSFAT1, WMO header
FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php.


FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 42.1N  41.9W   65 KT  75 MPH
 12H  06/1800Z 42.5N  40.7W   65 KT  75 MPH
 24H  07/0600Z 43.3N  38.4W   65 KT  75 MPH
 36H  07/1800Z 44.7N  35.6W   60 KT  70 MPH
 48H  08/0600Z 46.5N  32.9W   60 KT  70 MPH
 60H  08/1800Z 48.6N  31.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  09/0600Z 50.3N  31.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  10/0600Z 49.1N  32.4W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  11/0600Z 46.5N  25.4W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Roberts
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