ATL: HERMINE - Post-Tropical - Discussion

[galaxy401]

Peak strength is now forecast to be slightly higher.

[cycloneye]

TROPICAL DEPRESSION NINE DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016
1100 PM EDT SUN AUG 28 2016

Flight-level wind data from an earlier NOAA reconnaissance mission
along with WSR-88D Doppler radar data from Key West indicate that
the depression had been moving southwestward between 1800-0000 UTC.
However, the most recent radar data and nearby surface observations
suggest that the cyclone has now turned toward the west. The last
reliable wind data from the NOAA WP-3 recon aircraft supported an
intensity of 30 kt, and that intensity is being maintained for this
advisory given that the radar and satellite signatures haven't
improved. The central pressure of 1007 mb is based on a reliable
observation from ship WMKN, located just north of the center.

The initial motion estimate is 270/08 kt. Now that deep convection
has waned, the system has turned westward and this motion is
expected to continue for the next 24 hours or so. This short term
motion is supported by NOAA recon dropsonde data on the return leg
home, which indicated that 500 mb heights were 10-20 meters higher
over the southeastern Gulf of Mexico than what the global models
have been forecasting. After that time, the global and regional
models are in surprisingly good agreement on the cyclone slowing
down and turning toward the west-northwest and then northward in the
36- to 48-hour periods as the depression moves around the western
periphery of a narrow subtropical ridge that is expected to be
located over the Bahamas and South Florida at that time. By 72 hours
and beyond, the tropical cyclone is forecast to lift out and
accelerate to the northeast as a shortwave trough over the western
Great Lakes digs southeastward and captures the depression. The new
NHC forecast track has been shifted to the right of the previous
advisory track mainly due to the more southerly initial position,
and lies a little to the left of the consensus model TVCN.

Strong vertical shear that has been plaguing this system for the
past week is expected to gradually subside to less than 10 kt in
18-24 hours, which should allow for more organized deep convection
to develop. However, the southerly low-level inflow will still be
disrupted by the terrain of western Cuba until the cyclone moves
west of 85W longitude, which will then provide a straight trajectory
across the Yucatan Channel and into the low-level center. By 36
hours and beyond, the depression will moving over SSTs greater
than 30C and the light vertical wind shear is expected to back
around from a northerly to a southwesterly direction, which usually
favors more significant intensification. However, dry air in the
mid-/upper-levels noted in the recent 0000 UTC soundings from Key
West northward to the Gulf coast is expected be entrained into the
northwestern semicircle of the cyclone's circulation by 48 hours
and beyond, and this appears to be the main inhibiting factor to
strengthening by the global models. Given these mixed signals, the
NHC intensity forecast remains conservative and closely follows the
intensity model IVCN. The confidence in the intensity forecast
remains lower than usual for this system.

FORECAST POSITIONS AND MAX WINDS

INIT 29/0300Z 23.4N 82.7W 30 KT 35 MPH
12H 29/1200Z 23.5N 84.0W 30 KT 35 MPH
24H 30/0000Z 23.8N 85.4W 35 KT 40 MPH
36H 30/1200Z 24.4N 86.8W 35 KT 40 MPH
48H 31/0000Z 25.1N 87.1W 40 KT 45 MPH
72H 01/0000Z 27.0N 86.3W 45 KT 50 MPH
96H 02/0000Z 29.1N 82.9W 50 KT 60 MPH
120H 03/0000Z 31.2N 78.3W 50 KT 60 MPH

$$
Forecaster Stewart

[gatorcane]

Nice long discussion by Stewart for the 11pmest advisory

[SeGaBob]

Yep definitely no rain for here now...

[JaxGator]

NHC noted the WSW movement but now they say it's resumed it's W movement. Also the intensity forecast is slightly higher.

[chris_fit]

I knew this was a discussion by Forecaster Stewart even without looking at the bottom - Love his discussions.

[psyclone]

note the landfall point has moved from Dixie county southward to near the Levy/Citrus county border.

[gatorcane]

Shift to the right on the 11pm est track and slightly higher intensity. By the way, what a shortwave that is turning this NE for late August!

[Yellow Evan]

Shear should relax and waters are warm. Forecast intensity likely conservative IMO, as I could see a hurricane before landfall.

[gatorcane]

NHC mentions dry mid-level air as the only inhibiting factor. Let us hope it keeps this in check. By the way the Greater Tampa Bay Area is well within the cone of uncertainty.

[Michele B]

Shear should relax and waters are warm. Forecast intensity likely conservative IMO, as I could see a hurricane before landfall.

I agree, Evan. This system has fought off hardier "opposition" than it is now encountering, and is still alive!

The very warm waters of the Gulf is troubling....

[psyclone]

NHC mentions dry mid-level air as the only inhibiting factor. Let us hope it keeps this in check. By the way the Greater Tampa Bay Area is well within the cone of uncertainty.

we would get substantial weather with that track. a 50kt cyclone would likely be somewhat asymmetric and right loaded...giving the tampa bay area up to cedar key the worst. still, it's early and lots could change. I do think heavy rain is highly likely and sandbags are already being made available in the area.

[sponger]

I always take comfort being down the middle this far out. We will see what the track looks like Tuesday.

[NDG]

Shift to the right on the 11pm est track and slightly higher intensity. By the way, what a shortwave that is turning this NE for late August!

Is kind of hard to believe for this time of the year, but I wouldn't doubt if the track starts shifting westward if the TD ends up tracking more westward due to stronger ridging holding stronger to the north of it over the next couple of day.

[HurriGuy]

Shift to the right on the 11pm est track and slightly higher intensity. By the way, what a shortwave that is turning this NE for late August!

Is kind of hard to believe for this time of the year, but I wouldn't doubt if the track starts shifting westward if the TD ends up tracking more westward due to stronger ridging holding stronger to the north of it over the next couple of day.

Yeah especially when the dropsondes showed stronger ridging than the global models anticipated and that was only a 12 hour forecast and they were off. Makes you wonder.

[mobilebay]

Shift to the right on the 11pm est track and slightly higher intensity. By the way, what a shortwave that is turning this NE for late August!

Is kind of hard to believe for this time of the year, but I wouldn't doubt if the track starts shifting westward if the TD ends up tracking more westward due to stronger ridging holding stronger to the north of it over the next couple of day.

Yeah especially when the dropsondes showed stronger ridging than the global models anticipated and that was only a 12 hour forecast and they were off. Makes you wonder.

And thry responded by adjusting track to the right. Makes perfect since

[Sanibel]

The disturbance is still seriously inhibited by a hostile upper...

[psyclone]

If the system can actually get into a favorable environment and stack...watches...when they become necessary...could be of the hurricane variety rather than TS. but the system needs to serious work to warrant that. I think the current conservative stance is the best course of action. For folks up on the nature coast and big bend...even a tropical storm can cause significant water rises so concern is definitely justified.

[CrazyC83]

If the system can actually get into a favorable environment and stack...watches...when they become necessary...could be of the hurricane variety rather than TS. but the system needs to serious work to warrant that. I think the current conservative stance is the best course of action. For folks up on the nature coast and big bend...even a tropical storm can cause significant water rises so concern is definitely justified.

Since there are no watches in the Keys, I don't think they would be necessary until Tuesday or so.

[SeGaBob]

Any chance the track comes back west a bit? It's frustrating to see something get so close but yet so far.