Major Hurricane Helene

[TPAwx]

Another bonkers HAFS-B run in progress, grain of salt of course.  
 

That wind field and onshore flow with the 0z GFS would be suboptimal for the coastal counties of TB. 
 

 

[Radtechwxman]

This is the best PTC9 has looked so far

[GaWx]

0Z Euro a bit delayed in landfalling on the US vs earlier runs with 985 mb midnight Thu night Big Bend. Still 987 Athens Fri AM meaning hardly any weakening due to moving an avg of 25 mph!

————————

0Z UKMET: Apalachicola late Thu night then to Atlanta area in only ~12 hours due to moving on average ~25 mph!

TROPICAL DEPRESSION 09L ANALYSED POSITION : 18.1N 81.8W

ATCF IDENTIFIER : AL092024

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
0000UTC 24.09.2024 0 18.1N 81.8W 1003 32
1200UTC 24.09.2024 12 19.7N 83.9W 1003 36
0000UTC 25.09.2024 24 19.8N 85.6W 999 36
1200UTC 25.09.2024 36 21.3N 86.4W 995 41
0000UTC 26.09.2024 48 22.9N 86.5W 992 39
1200UTC 26.09.2024 60 24.8N 86.1W 991 43
0000UTC 27.09.2024 72 28.1N 85.5W 988 52
1200UTC 27.09.2024 84 31.9N 84.8W 989 37
0000UTC 28.09.2024 96 37.0N 85.8W 994 24
1200UTC 28.09.2024 108 40.2N 90.4W 1000 25
0000UTC 29.09.2024 120 CEASED TRACKING

[hawkeye_wx]

I don't see much organization tonight.  A blast of sw shear is preventing mid-level and surface alignment.

[dan11295]

I wonder if the current board nature of the system will stop it from organizing too quickly. Also until the shear actually drops over the system its not doing to get going. Radar looks less impressive than a few hours ago.

[Seminole]

1 hour ago, dan11295 said:

I wonder if the current board nature of the system will stop it from organizing too quickly. Also until the shear actually drops over the system its not doing to get going. Radar looks less impressive than a few hours ago.

ULL has yet to retrograde. Until it does PTC9 will be slow to develop. The EURO seems to have a good handle on this. 

[hawkeye_wx]

The latest hurricane models are still bombing this thing over the loop current.  What I don't understand is why these models continue to try to strengthen it so much today.  I get that there is a disconnect when the system does not yet have a well-organized center, but why do these models seemingly not see the current shear?

[40/70 Benchmark]

55 minutes ago, Seminole said:

ULL has yet to retrograde. Until it does PTC9 will be slow to develop. The EURO seems to have a good handle on this. 

I wonder if ultimately all this delay does is act to pushback any ERC until near landfall, if at all.

[Hotair]

2 minutes ago, hawkeye_wx said:

The latest hurricane models are still bombing this thing over the loop current.  What I don't understand is why these models continue to try to strengthen it so much today.  I get that there is a disconnect when the system does not yet have a well-organized center, but why do these models seemingly not see the current shear?

Perhaps a reminder not to put too much weight on models prior to the storm becoming a proper tropical storm.  Even then strength predictions can be quite tricky. I would ignore most models for now until this is TS Helene 

[CoastalWx]

Shear is still impacting this. The oblong shape on satellite is a dead giveaway. 
 

The euro seems to show this as it seems like it wants to have an eye open to the SW along its entire journey. Hence the weaker pressure. 
 

It will go over explosive fuel, but I’m not sure how shear will try to counteract that. It is important to note that some models are predicting RI. Haven’t had a chance to look at SHIPS guidance, but the 700-500RH and RI statistics are good pieces to look at on SHIPS.

[40/70 Benchmark]

9 minutes ago, CoastalWx said:

Shear is still impacting this. The oblong shape on satellite is a dead giveaway. 
 

The euro seems to show this as it seems like it wants to have an eye open to the SW along its entire journey. Hence the weaker pressure. 
 

It will go over explosive fuel, but I’m not sure how shear will try to counteract that. It is important to note that some models are predicting RI. Haven’t had a chance to look at SHIPS guidance, but the 700-500RH and RI statistics are good pieces to look at on SHIPS.

I love using 700-500RH....often reveals subtle red flags in guidance that are not always reflected well im raw intensity output....kind of a akin to clown maps dropping a 20" snowgasm only to notice razor thin warm layers and/or drier air at 700-800mb.

[SnowGoose69]

8 minutes ago, CoastalWx said:

Shear is still impacting this. The oblong shape on satellite is a dead giveaway. 
 

The euro seems to show this as it seems like it wants to have an eye open to the SW along its entire journey. Hence the weaker pressure. 
 

It will go over explosive fuel, but I’m not sure how shear will try to counteract that. It is important to note that some models are predicting RI. Haven’t had a chance to look at SHIPS guidance, but the 700-500RH and RI statistics are good pieces to look at on SHIPS.

The NHC track looks exactly like the Euro too.  I have found in recent years NHC focuses more as far as track on the Euro as well as the HWRF/HMON.  Those other spaghetti models just seem more often to be ignored now by them or considered less.  It’s clear they’re not buying the N-NNW movement after landfall, at least not til the system is weaker hours later.  That NNW movement idea to me only would work if this comes in as a weak mess.  If it’s a strong 2 or higher it’s going to move E of N for awhile after landfall despite any upper low to the west 

[NorthHillsWx]

I actually think it looks a whole lot better overall. It’s developed banding on the eastern side and on satellite it looks like the thunderstorms have consolidated into a singular mass vs popcorn storms. “Center” is west of main convection but otherwise this looks closer to a TS than last night. Westerly shear is clearly a factor at this stage. So far, Euro seems to be handling development the best. I am not sure early development matters as much. The best conditions this system encounters will be north of Cuba as it parallels the Florida coast. I’d look for a tight COC and a well formed CDO if RI is to happen. Actual strength leaving the carribean will not matter much on the overall ceiling this system has given the POTENTIAL for RI. I’m more concerned with the structure and shear from the upper level system to the west

[hawkeye_wx]

The 06z Euro actually moves the center over the northeast tip of the Yucatan, where it only slowly moves for about 12 hours. 

Also, while the hurricane models insist on bombing it out over the eastern gulf, the Euro barely strengthens it at all.

[40/70 Benchmark]

6 minutes ago, hawkeye_wx said:

The 06z Euro actually moves the center over the northeast tip of the Yucatan, where it only slowly moves for about 12 hours. 

I was just noticing that...about 25% of the ensembles do, as well...a few GEFS members do, too.

[SnowGoose69]

4 minutes ago, wthrmn654 said:

They love love LLLOOVVVEEE the concensus model thingy and always mention it in there discussions. 

Definitely have noticed that but so often seems the track is some combo of the Euro/GFS/HWRF

[beanskip]

So what's the most a tropical system has strengthened in 60 hours? 

I know when (if?)  the shear fades it will be a great environment, but at some point the clock becomes a factor, right? 

Looks like hurricane hunters can't find anything under 1000 mb yet. 

 

[SnowGoose69]

2 minutes ago, beanskip said:

So what's the most a tropical system has strengthened in 60 hours? 

I know when (if?)  the shear fades it will be a great environment, but at some point the clock becomes a factor, right? 

Looks like hurricane hunters can't find anything under 1000 mb yet. 

 

Wilma I think was fastest it was a TS to a 5 in like 22 hours or something close to that.  There’s been many that have gone TS to a 3 or 4 relatively fast as well  

[dbullsfan]

Supposed to be going to a concert at the Amphitheater in Tampa Thursday night, was worried but looking like we should be in the clear outside of some outer bands so it might get a little wet. I know it’s a storm so things can always change but it seems the models haven’t budged for a couple days now and are almost locked in agreement.


.

[40/70 Benchmark]

1 minute ago, beanskip said:

So what's the most a tropical system has strengthened in 60 hours? 

I know when (if?)  the shear fades it will be a great environment, but at some point the clock becomes a factor, right? 

Looks like hurricane hunters can't find anything under 1000 mb yet. 

 

I think there is about a 12 hour window for potential RI during the day on Thursday, after the core is well established and its over the loop current before some drier air begins getting entrained the final few hours prior to LF....probably from about 00z Thursday and onward.

[dan11295]

IR still looks a bit disorganized, but some banding is showing up on Cayman radar under the northern convection.

[hawkeye_wx]

The visible loop shows the surface circulation is becoming better defined.  The center is right on the west edge of the convection.  The recon extrap pressure is now creeping under 1000 mb.

[WxWatcher007]

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. 

[40/70 Benchmark]

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.

[SnowGoose69]

Early 12Z guidance definitely a couple less far west benders over GA.  Thats very close to NHC/Euro tracks

 

[Seminole]

14 minutes ago, 40/70 Benchmark said:

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

After that all model guidance has 30 to 40 knot shear depicted. 

[40/70 Benchmark]

Just now, Seminole said:

After that all model guidance has 30 to 40 knot shear depicted. 

Looks to me like it has a window of nearly ideal conditions on Thursday.

[jbenedet]

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.

[purduewx80]

6 minutes ago, Seminole said:

After that all model guidance has 30 to 40 knot shear depicted. 

Is that shear in the room with us? This is an ideal setup for ventilation and expansive outflow in at least three quadrants. 

[Hotair]

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