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Major Hurricane Helene


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1 minute ago, WxWatcher007 said:

Much like in the Gulf, shear vector and storm motion matter a lot in how much shear a TC actually encounters. It looks like a shift in shear direction has now given this the space to organize. Just look at visible satellite from yesterday vs now.

Tail Doppler shows that the LLC and MLC are pretty well aligned. That likely means the organizational trend (not necessarily intensity, yet) is poised to pick up the pace—if alignment holds. 

I think we see slow, steady intensification for the next 36-48 hours.

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The fast track is misleading to fresh water flooding risks. The heavy rain starts tomorrow in Florida panhandle and doesn’t stop for 30 hrs. 

The interaction with the strong ULL will enhance and prolong the rains, as if this was actually a slow mover.

Regardless of exact landfall I think Tallahassee is in an especially vulnerable spot in this regard.

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Helene is born. Will there be a new thread ? Or rename this one ?

 

062 
WTNT34 KNHC 241458
TCPAT4

BULLETIN
Tropical Storm Helene Advisory Number   5
NWS National Hurricane Center Miami FL       AL092024
1100 AM EDT Tue Sep 24 2024

...TROPICAL STORM HELENE FORMS OVER THE NORTHWESTERN CARIBBEAN
SEA...
...HURRICANE AND STORM SURGE WATCHES REMAIN IN EFFECT FOR PORTIONS
OF THE FLORIDA GULF COAST...


SUMMARY OF 1100 AM EDT...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...19.5N 84.3W
ABOUT 180 MI...295 KM ESE OF COZUMEL MEXICO
ABOUT 170 MI...275 KM SSE OF THE WESTERN TIP OF CUBA
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

A Tropical Storm Warning has been issued for the Lower Florida Keys
west of the Seven Mile Bridge and for the Dry Tortugas.

A Tropical Storm Watch has been issued for the Middle Florida Keys
from the Seven Mile Bridge to the Channel 5 Bridge.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Storm Surge Watch is in effect for...
* Indian Pass southward to Flamingo
* Tampa Bay
* Charlotte Harbor

A Hurricane Watch is in effect for...
* Cabo Catoche to Tulum, Mexico
* Cuban province of Pinar del Rio
* Englewood to Indian Pass
* Tampa Bay

A Tropical Storm Warning is in effect for...
* Dry Tortugas
* Lower Florida Keys west of the Seven Mile Bridge
* Grand Cayman
* Rio Lagartos to Tulum, Mexico
* Cuban provinces of Artemisa, Pinar del Rio, and the Isle of Youth

A Tropical Storm Watch is in effect for...
* Middle Florida Keys from the Seven Mile Bridge to the Channel 5
Bridge
* Flamingo to south of Englewood
* West of Indian Pass to Walton Bay County line

A Storm Surge Watch means there is a possibility of life-
threatening inundation, from rising water moving inland from the
coastline, in the indicated locations during the next 48 hours.
For a depiction of areas at risk, please see the National Weather
Service Storm Surge Watch/Warning Graphic, available at
hurricanes.gov.

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area within the next 36 hours.

A Hurricane Watch means that hurricane conditions are possible
within the watch area.  A watch is typically issued 48 hours
before the anticipated first occurrence of tropical-storm-force
winds, conditions that make outside preparations difficult or
dangerous.

A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.

Wind and storm surge warnings will likely be required for the 
U.S. later today.

For storm information specific to your area in the United
States, including possible inland watches and warnings, please
monitor products issued by your local National Weather Service
forecast office. For storm information specific to your area
outside of the United States, please monitor products issued by
your national meteorological service.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM EDT (1500 UTC), the center of Tropical Storm Helene was
located near latitude 19.5 North, longitude 84.3 West.  Helene is
moving toward the northwest near 12 mph (19 km/h), and this 
general motion is expected to continue through early Wednesday.  A 
northward to north-northeastward motion at a faster forward speed 
is expected on Wednesday and Thursday.  On the forecast track, the 
center of Helene will move across the far northwestern Caribbean 
Sea through tonight, and then move across the eastern Gulf of 
Mexico Wednesday and Thursday, potentially reaching the Gulf coast 
of Florida late Thursday.

Data from an Air Force Reserve Hurricane Hunter aircraft indicate 
that the system has acquired a well-defined center of circulation, 
and maximum sustained winds have increased to near 45 mph (75 km/h) 
with higher gusts.  Additional strengthening is forecast, and 
Helene is expected to become a hurricane on Wednesday.  Continued 
strengthening is anticipated after that time, and Helene could 
become a major hurricane on Thursday.

Tropical-storm-force winds extend outward up to 140 miles (220 km)
to the east of the center.

Data from the Hurricane Hunter aircraft indicate that the minimum 
central pressure is 1000 mb (29.53 inches).


HAZARDS AFFECTING LAND
----------------------
Key Messages for Helene can be found in the Tropical Cyclone
Discussion under AWIPS header MIATCDAT4 and WMO header WTNT44 KNHC
and on the web at hurricanes.gov/text/MIATCDAT4.shtml

RAINFALL: Helene is expected to produce total rain accumulations of
4 to 8 inches over western Cuba and the Cayman Islands with isolated
totals around 12 inches. Over the eastern Yucatan Peninsula, 4 to 6
inches of rain are expected with isolated totals over 8 inches. This
rainfall brings a risk of considerable flooding.

Over the Southeastern U.S., Helene is expected to produce total rain
accumulations of 4 to 8 inches with isolated totals around 12
inches. This rainfall will likely result in areas of considerable
flash and urban flooding, with minor to moderate river flooding
likely, and isolated major river flooding possible.

For a complete depiction of forecast rainfall associated with
Helene, please see the National Weather Service Storm Total Rainfall
Graphic, available at hurricanes.gov/graphics_at4.shtml?rainqpf and
the Flash Flood Risk graphic at
hurricanes.gov/graphics_at4.shtml?ero.

STORM SURGE: The combination of a dangerous storm surge and the
tide will cause normally dry areas near the coast to be flooded by
rising waters moving inland from the shoreline.  The water could
reach the following heights above ground somewhere in the indicated
areas if the peak surge occurs at the time of high tide...

Ochlockonee River, FL to Chassahowitzka, FL...10-15 ft
Chassahowitzka, FL to Anclote River, FL...6-10 ft
Indian Pass, FL to Ochlockonee River, FL...5-10 ft
Anclote River, FL to Middle of Longboat Key, FL...5-8 ft
Tampa Bay...5-8 ft
Middle of Longboat Key, FL to Englewood, FL...4-7 ft
Englewood, FL to Bonita Beach, FL...3-5 ft
Charlotte Harbor...3-5 ft

For a complete depiction of areas at risk of storm surge inundation,
please see the National Weather Service Peak Storm Surge Graphic,
available at hurricanes.gov/graphics_at4.shtml?peakSurge.

Storm surge could raise water levels by as much as 2 to 4 feet above
normal tide levels in areas of onshore winds along the southern
coast of Pinar del Rio, Cuba, including the Isle of Youth.

Storm surge could raise water levels by as much as 2 to 4 feet above
ground level in areas of onshore winds within the warning area along
the east coast of the Yucatan Peninsula.

WIND: Hurricane conditions are possible within the watch areas in
Cuba and Mexico by early Wednesday.  Hurricane conditions are
possible within the U.S. watch areas Wednesday night and early
Thursday.  Tropical storm conditions are expected in the warning
areas in the Cayman Islands, Cuba, and Mexico today.  Tropical
storm conditions are expected in the warning area in the Lower
Florida Keys beginning on Wednesday, and are possible in the watch
area in the Middle Florida Keys beginning late Wednesday.

SURF: Swells generated by Helene will affect the southern coast
of Cuba and the Yucatan Peninsula of Mexico during the next couple
of days.  Swells will spread northward toward the west coast of
Florida and the northeastern Gulf Coast on Wednesday and Thursday.
These swells are likely to cause life-threatening surf and rip
current conditions.  Please consult products from your local weather
office.


NEXT ADVISORY
-------------
Next intermediate advisory at 200 PM EDT.
Next complete advisory at 500 PM EDT.

$$
Forecaster Berg
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Tropical Storm Helene Discussion Number   5
NWS National Hurricane Center Miami FL       AL092024
1100 AM EDT Tue Sep 24 2024

An Air Force Reserve Hurricane Hunter measured peak 925-mb
flight-level winds of 52 kt to the northeast of the center, which
supports an initial intensity of 40 kt.  Dropsonde data also
indicated that the central pressure is down to 1000 mb. Very 
recently, data from the plane and one-minute visible satellite 
imagery indicate that the center has become better defined. Based 
on these data, the system is being designated as Tropical Storm 
Helene at this time.

Helene is moving a little faster toward the northwest (310/10 kt) 
as it moves around a mid-level area of high pressure located over 
Florida and the Southeastern U.S.  The high is expected to slide 
eastward through Wednesday as a deep-layer trough digs southward 
over the Lower Mississippi Valley.  This pattern evolution should 
cause the system to turn northward and north-northeastward late 
Wednesday into Thursday.  The track guidance is very tightly 
clustered, which would normally imply high forecast confidence.  
However, depending on exactly where the center forms could end up 
shifting the entire guidance suite in future cycles, so it is 
imperative to not focus on specific landfall locations this far in 
the future.

Satellite trends suggest that the shear over the system is
beginning to decrease, and model guidance continues to show
relatively low to moderate shear for the next 48 hours or so.  In
addition, oceanic heat content values are very high, and the system
will be moving through an environment of upper-level divergence.
Therefore, significant strengthening is anticipated, and the NHC
intensity forecast shows the system reaching a peak intensity
around 100 kt in 48 hours while over the eastern Gulf of Mexico.
There could be some increase in shear around the time the system
reaches the coast, given the system's large size, it might only
weaken slowly.  As a result, there is still a risk that the system
could reach the coast as a major hurricane.

Helene's forecast radii are at the 90th percentile of hurricane
size at similar latitudes.  Due to the forecast large size of this
system, storm surge, wind, and rainfall impacts will extend well
away from the center, particularly on the east side.  In addition,
the fast forward speed while it crosses the coast will likely result
in farther inland penetration of strong winds over parts of the
southeastern United States after landfall.
FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 19.5N  84.3W   40 KT  45 MPH
 12H  25/0000Z 20.3N  85.2W   50 KT  60 MPH
 24H  25/1200Z 21.5N  86.3W   65 KT  75 MPH
 36H  26/0000Z 23.2N  86.3W   80 KT  90 MPH
 48H  26/1200Z 25.9N  85.4W  100 KT 115 MPH
 60H  27/0000Z 29.7N  84.3W  100 KT 115 MPH
 72H  27/1200Z 33.9N  83.9W   45 KT  50 MPH...INLAND
 96H  28/1200Z 39.7N  86.8W   20 KT  25 MPH...POST-TROPICAL
120H  29/1200Z...DISSIPATED

$$
Forecaster Berg
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Interesting Satellite loop (time sensitive) as center continues to drift sw away from deepest convection.

No doubt there are TS winds associated with all the convection to the NE of the LLC so I get the upgrade.

Will be interesting to see if convection develops over current LLC or new enter forms under the deep convection.

ULL over the Yucatan is backing NW but there is clearly still SW shear affecting Helene.  Interesting to watch this develop.

I would not be surprised to see nudges east in the track over the next 24 hours or so.  Either way depending on how fast Helene can intensify the current track (depending on intensity) could push A LOT of water onto the west coast of FL, especially from just south of Tampa northward.

 

Link to visible loop:

https://www.meteo.psu.edu/ewall/PSUGOES_MESO1/loop60.html

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3 minutes ago, hooralph said:

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

Proactive and appropriate IMO for a coastal/low lying county and area.  Not in the current cone but as others as noted Helene will push a significant surge along the FL West Coast.

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22 minutes ago, hooralph said:

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

Their Facebook page includes homes that don’t meet 1995 building codes in the order. Seems excessive to me, that's a lot of homes, and there's quite a bit of confusion in the comments.

IMG_5155.thumb.jpeg.0bd032819f7d5ec3c97a6ab41276222d.jpeg

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24 minutes ago, hooralph said:

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

Very appropriate considering the unknowns and the certainty that this event will happen mid week without the luxury for most to prepare over a weekend.

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12Z CMC: 977 Big Bend Thu night, but it only weakens to 978 mb SE of Atlanta! That would be bordering on alltime record low SLPs in that region of GA. The potential damage well inland should not be understated.

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10 minutes ago, GaWx said:

12Z CMC: 977 Big Bend Thu night, but it only weakens to 978 mb SE of Atlanta! That would be bordering on alltime record low SLPs in that region of GA. The potential damage well inland should not be understated.

Significant -NAO patterns are good for displacing climatological patterns. This syntopic interaction and extra tropical transition is common to what is experienced in the northeast; unusual in the southeast…

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The inland flooding could be devastating with the PRE and Helene combo. Southern Appalachian areas could see as much impact as Florida with flash flooding, mud slides, and high winds in the higher elevations. Some areas along the Blue Ridge could easily see 12-16" of rain with orographic uplift with the SE flow

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12 minutes ago, GaWx said:

12Z CMC: 977 Big Bend Thu night, but it only weakens to 978 mb SE of Atlanta! That would be bordering on alltime record low SLPs in that region of GA. The potential damage well inland should not be understated.

Yeah, call me skeptical. Never seen a TC that didn’t begin weakening rapidly upon LF.

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