[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 100247
TCDAT3

Hurricane Lee Discussion Number  19
NWS National Hurricane Center Miami FL       AL132023
1100 PM AST Sat Sep 09 2023

While the geostationary satellite appearance of Lee has not changed
appreciably since the prior advisory, data from a NOAA P-3
reconnaissance mission in the storm, in addition to earlier GPM and
SSMIS microwave imagery, indicate that Lee is in the middle of an
eyewall replacement cycle (ERC). The aircraft has been reporting
both an inner and outer eyewall, with the outer eyewall gradually
contracting in size. However, this outer eyewall continues to
exhibit some asymmetry, consistent with modest vertical wind shear
still affecting the storm. In addition, the aircraft has reported
that the inner-core wind field is becoming weaker, but broader, with
a more muted wind profile outside of the radius of maximum wind.
This observation is also evident comparing TDR data between the
morning and evening NOAA-P3 missions. The peak 700 mb flight level
winds were down to 94 kt, with SFMR only in the 75-85 kt range. The
initial intensity has been adjusted to a somewhat generous 90 kt for
this advisory.

Lee continues to move west-northwestward this evening at 300/9 kt.
As discussed previously, the mid-level ridge axis currently north of
Lee is soon expected to shift to its west-southwest, resulting in
Lee slowing its forward motion, and perhaps making a slight westward
bend over the next 24-36 hours. Afterwards, an eastward-moving
mid-latitude trough is expected to erode this ridge and allow Lee to
turn northward by the end of the forecast period. There remains a
significant amount of spread in both the deterministic and ensemble
guidance on when this turn occurs, and then how quickly Lee
accelerates northward. For now the NHC track forecast remains
closest to the consensus aids, which have slowed a bit from the
prior cycle, and the latest track forecast is a bit slower but near
the same trajectory as the prior advisory.

While vertical wind shear over Lee appears to be gradual decreasing
over the system, the ongoing ERC seems to be resulting in the wind
field broadening versus allowing Lee to re-intensify so far.
However, once this cycle is complete, reintensification is still
anticipated, and the NHC intensity forecast still takes Lee back to
a category 4 hurricane in 36-48 hours, in good agreement with the
latest HAFS-A/B forecasts, which both explicitly show the ongoing
ERC. However, Lee's growing wind field, in combination with its
slowing forward motion, could make the hurricane susceptible to
feeling the effects of its own cold wake, which the
atmospheric-ocean coupled HAFS and HWRF models suggest could begin
to occur beyond 36 hours. Thus, the latest NHC intensity forecast
shows gradual weakening beginning by that time, with more pronounced
weakening by the end of the forecast period as the hurricane
traverses already cooled sea-surface temperatures from Franklin and
Idalia last week along its forecast track. This intensity forecast
is in good agreement with the simple consensus aids, but is a little
lower than the HFIP corrected consensus early on.


KEY MESSAGES:

1. Lee's core is expected to move well north of the northern
Leeward Islands, the Virgin Islands, and Puerto Rico this weekend
and early next week.

2. Dangerous surf and life-threatening rip currents are affecting
portions of the northern Leeward Islands.  These conditions are
spreading westward and northward and will affect Puerto Rico,
Hispaniola, the Turks and Caicos, the Bahamas, and Bermuda during
the next several days.

3. It remains too soon to know what level of impacts, if any, Lee
might have along the U.S. East Coast, Atlantic Canada, or Bermuda
late next week, especially since the hurricane is expected to slow
down considerably over the southwestern Atlantic.  Regardless,
dangerous surf and rip currents are expected along most of the U.S.
East Coast beginning tomorrow and continuing into next week as Lee
grows in size. Users should continue to monitor updates to the
forecast of Lee during the next several days.


FORECAST POSITIONS AND MAX WINDS

INIT  10/0300Z 21.0N  59.9W   90 KT 105 MPH
 12H  10/1200Z 21.6N  60.9W  100 KT 115 MPH
 24H  11/0000Z 22.4N  62.3W  110 KT 125 MPH
 36H  11/1200Z 23.0N  63.5W  120 KT 140 MPH
 48H  12/0000Z 23.3N  64.7W  115 KT 130 MPH
 60H  12/1200Z 23.6N  65.6W  110 KT 125 MPH
 72H  13/0000Z 24.0N  66.6W  105 KT 120 MPH
 96H  14/0000Z 25.6N  68.0W   95 KT 110 MPH
120H  15/0000Z 28.8N  68.3W   85 KT 100 MPH

$$
Forecaster Papin
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