Hurricane Helene,Analysis,Sat Pics,Models Thread

[wxman57]

Not much change in the 18Z models. I've weeded out the climo models, statistical models, and the BAM runs, as they shouldn't really be looked at for guidance. The remaining models continue to indicate recurvature between 55W-58W, perhaps a little farther east of the 12Z runs. Helene has been tracking right of model guidance for days. No reason to think it's any threat to the east U.S. coast. Slight chance of a Bermuda threat, better chance of a threat in eastern Canada/Newfoundland.

Oh, that one lone track moving WNW (brown color) is the interpreted version of the 18Z AVN run (AVNI). I wouldn't put much faith in it.

[WeatherTracker]

Can you link that graphic above? thank you

[Thunder44]

I saw the 12z ECMWF on the Plymouth site. It looks very much like the NOGAPS. It takes to just SE of Bermuda in 7 days around 60N.

[hial2]

HURRICANE HELENE (AL082006) ON 20060916

18:00z Models.terstorm1012 they dont pass it more than 61 west as I dont count the A98E.[/quote

I remember yesterday @ this time that no model took it past 43 west..I question the reliabality/accuracy of models when they are off by such a wide margin in a short amount of time...IMO,we place too much emphasis on them..

Not past 43 W?

Here is yesterdays 1200z

TROPICAL STORM HELENE (AL082006) ON 20060914 1200 UTC

I was wrong about the time frame..But not what I said...And weren't all the models close together at one point? I remember reading from a pro that it was highly unusual for all the models to be clustered in that manner..and now..

[Damar91]

Ok, here's a stupid question. Lane's moisture will be moving in the general direction of the trough of low pressure. Could that interaction have any effect on the trough itself, therefore effecting Helene. Stupid question, I know but I was just curious. Thanks!

Anyone?

[storms in NC]

wx57 could you put up a steering map

[NESDIS Met]

Not much change in the 18Z models. I've weeded out the climo models, statistical models, and the BAM runs, as they shouldn't really be looked at for guidance. The remaining models continue to indicate recurvature between 55W-58W, perhaps a little farther east of the 12Z runs. Helene has been tracking right of model guidance for days. No reason to think it's any threat to the east U.S. coast. Slight chance of a Bermuda threat, better chance of a threat in eastern Canada/Newfoundland.

Oh, that one lone track moving WNW (brown color) is the interpreted version of the 18Z AVN run (AVNI). I wouldn't put much faith in it.

Ok Cowboy, if the 5 18z runs that take Helene west of 60 prior to recurvature "shouldn't really be looked at for guidance", why do they still exist?

I'm an old guy looking for a serious, scientific response. If you can't provide that please don't bother responding.

[linkerweather]

I wouldn't necessarily \"throw them out" but the BAM models are tropical models and have a very difficult time with mid latitude weather systems. i.e fronts and troughs from the continental US and into the corresponding latitude over the atlantic. That suite of models is a useful tool for systems farther south or ones that will end up farther south. Caribbean, GOM, Atlantic south of 20-25 N

[NESDIS Met]

I wouldn't necessarily \"throw them out" but the BAM models are tropical models and have a very difficult time with mid latitude weather systems. i.e fronts and troughs from the continental US and into the corresponding latitude over the atlantic. That suite of models is a useful tool for systems farther south or ones that will end up farther south. Caribbean, GOM, Atlantic south of 20-25 N

I appreciate the reasoning, thanks for reply.

I do see, however, that some of the globals (GFS and EURO) are beginning to latch onto the possibility that laminar-based height rises to the north of Helene could possibly trump the teleconnection-based solutions that we have seen thus far.

Looks like we're sort of in a middle period where the earlier teleconnections favorable to recurvature are shifting toward less-favorable based on a better resolution of some of the laminar flow models...that these higher resolution near-term solutions are starting to affect the wider-in-scope globals.

[WeatherTracker]

Hurricane Helene Discussion Number 18

Statement as of 5:00 PM EDT on September 16, 2006



Dvorak estimates from TAFB and SAB have not changed and a ragged eye
has been observed this afternoon in the visible imagery. CIMSS
experimental advanced Dvorak technique also suggests minimal
hurricane intensity. Thus...a 65 kt initial intensity is retained.
Today...a NOAA salex...Saharan air layer Experiment...mission on
the G-IV aircraft has been taking observations in the periphery of
Helene. While these dropwindsondes are showing substantial dry
air...CIRA precipitable water analyses suggest that sufficient
moisture is found in the system's inner core. Because of 27.5 c
SSTs...light/moderate vertical shear...and a moist environment...
continued slow intensification is anticipated. After two days...
both the shear and SSTs increase. Because of these conflicting
environmental factors...Helene is projected to peak in intensity
near 85 kt at days 2 and 3 with slight weakening thereafter. It is
noted that the GFDL model fields retain weaker shear into longer
lead times than the global models. The official forecast is
slightly above the Standard SHIPS model due to the influence of an
enhancing microwave predictor in the experimental SHIPS-microwave
model and is slightly below the previous prediction.

Current motion is estimated to be 310/11. Helene is moving toward a
break in the west-southwest to east-northeast oriented subtropical
ridge axis. After day 2...there is a large model divergence in the
track of Helene. The GFDL and UK quickly accelerate the system to
the north in advance of a strong short wave moving off of the US
Atlantic Seaboard. In contrast...the GFS...the GFS ensemble and
the ECMWF models turn Helene to the west-northwest and do not have
it picked up by the short wave trough. The NOGAPS and GFDN
models...as well as consensus approaches...split the difference.
As it is difficult to know which group will be correct...the track
forecast depicted here is close to the CONU consensus and is
slightly slower and just to the right of the previous forecast.
Perhaps with the model assimilation of the salex dropwindsondes...
the large model differences will be reduced in the next forecast
cycle.

Forecast positions and Max winds

initial 16/2100z 19.3n 46.3w 65 kt
12hr VT 17/0600z 20.0n 47.4w 70 kt
24hr VT 17/1800z 20.9n 48.7w 80 kt
36hr VT 18/0600z 21.8n 49.8w 85 kt
48hr VT 18/1800z 22.6n 51.0w 85 kt
72hr VT 19/1800z 24.0n 53.5w 85 kt
96hr VT 20/1800z 26.0n 56.0w 80 kt
120hr VT 21/1800z 29.0n 57.5w 75 kt

[WeatherTracker]

Tropical Storm Public Advisory

Statement as of 5:00 PM AST on September 16, 2006



...Helene continues toward the northwest with no change in
intensity...
At 500 PM AST...2100z...the center of Hurricane Helene was located
near latitude 19.3 north...longitude 46.3 west or about 1100 miles
...1775 km...east of the northern Leeward Islands.

Helene is moving toward the northwest near 13 mph...20 km/hr...and
this motion is expected to continue during the next 24 hours.

Maximum sustained winds are near 75 mph...120 km/hr...with higher
gusts. Some strengthening is forecast during the next 24 hours.

Hurricane force winds extend outward up to 30 miles...45 km...from
the center...and tropical storm force winds extend outward up to 175
miles...280 km.

Estimated minimum central pressure is 987 mb...29.15 inches.

Repeating the 500 PM AST position...19.3 N...46.3 W. Movement
toward...northwest near 13 mph. Maximum sustained winds...75 mph.
Minimum central pressure...987 mb.

The next advisory will be issued by the National Hurricane Center at
1100 PM AST.

$$
Forecaster Beven/landsea

[WeatherTracker]

[wxman57]

Ok Cowboy, if the 5 18z runs that take Helene west of 60 prior to recurvature "shouldn't really be looked at for guidance", why do they still exist?

I'm an old guy looking for a serious, scientific response. If you can't provide that please don't bother responding.

The "model runs", as they're typically referred to here are no more than basic guidance tools, designed for use in low-latitudes where incipient storms are being steered westward by relatively constant flow beneath the Bermuda High. But let's take a look at them:

BAM (BAMS, BAMM, and BAMD) -- the Beta and Advection Model. It's a simple trajectory model that uses the latest GFS run as a base, removing the storm's vortex to see where the current flow would take the storm. The BAM models look at the steering flow at 3 levels - shallow (BAMS), medium (BAMM), and deep (BAMD). The problem with the BAM models is that they don't account for changes in the steering flow in the future. They're not dynamic. They work well when the flow isn't changing, like inthe deep tropics, but poorly farther north where trofs/ridges are moving across the path of the storm. Since we're looking at just such trof/ridge interactions with Helene, the BAM models should be discarded.

I have no idea why the LBAR model (Limited area sine transorm BARatropic) is still included in any guidance. It's generally one of the poorest performing models, if not THE poorest performing model each year. If it's ever right, it's an accident.

That leaves the A98E, a purely statistical/climatological model that mostly just considers where past storms in the same region at the same time of year tracked. Totally worthless for guidance, unless the exact same weather pattern is in place as with the past storms in the same area.

So there you have it, those public model runs should only be used in the very deep tropics (south of 15N, generally) for developing storms that are trapped beneath the Bermuda High or in situations where the steering currents aren't changing over the 5-day track. Otherwise, they're of little value. The NHC runs them automatically every 6 hours, regardless of their value. Why? Ask them...

Does that answer your quesitons?

Now, that said, I do have some concerns that Helene could impact Bermuda significantly. Several runs of the GFS indicate that Helene may miss the 2nd trof around 50-55W and could continue westward until the third and largest trof reaches the storm around Bermuda's longitude. Most of the tropical models don't agree with the GFS at present. But the GFS was the first model to indicate that Ernesto may be a threat to Florida, and it was discarded for that.

So if you're in Bermuda, better not turn your back on Helene. If you're on the east U.S. Coast, that next big trof/front toward the end of next week should prevent Helene from reaching you.

[HenkL]

The latest ECMWF 12Z run indicates a slowly moving Helene from Wednesday on, going to the NW and reaching 30N 60W on Saturday.

[Pebbles]

The "model runs", as they're typically referred to here are no more than basic guidance tools, designed for use in low-latitudes where incipient storms are being steered westward by relatively constant flow beneath the Bermuda High. But let's take a look at them:

This has to win the award for one of the easiest to understand discriptions I have ever read here of when and how to take these models into consideration and when to throw them to the wayside and the whys for that!

FANTASTIC post!

[storms in NC]

So if you're in Bermuda, better not turn your back on Helene. If you're on the east U.S. Coast, that next big trof/front toward the end of next week should prevent Helene from reaching you.

I know it will not go to the east coast. But fronts have a funny way. Some times they move in faster or slower. So I don't count nothing out till it is in stone.

[storms in NC]

Just looking at the vloop zoom. You can see it took a big jog to the west.

http://www.ssd.noaa.gov/goes/flt/t3/loop-vis.html

[storms in NC]

http://iwave.rsmas.miami.edu/surf/images/tanal.1.gif

[Evil Jeremy]

wow! your right! and by looking at this: http://www.ssd.noaa.gov/goes/flt/t3/loop-wv.html an eye is trying to form now! the next 12 hours can be very improtant to its overall future track.

[SouthFloridawx]

wow! your right! and by looking at this: http://www.ssd.noaa.gov/goes/flt/t3/loop-wv.html an eye is trying to form now! the next 12 hours can be very improtant to its overall future track.

With all due respect, I do not think a few hours tonight is going to alter the eventual coures. Fish storm with a possible effects on Bermuda and a very slight outside chance on the Islands.