Tropical Weather Briefing #1, Week of September 18

GEORGE KASICA - 9/18/2006 11:19 AM

Tropical Weather Briefing #1, Week of September 18 

Forecaster: Kasica

Basin: Atlantic

Storm: Hurricane Helene

At 15Z Hurricane Helene is currently located at 23.2N  50.2W with winds of  110KT. (See Discussion #25 at  http://www.nhc.noaa.gov/text/refresh/MIATCDAT3+shtml/181435.shtml limited shelf life warning applies)  
Currently the storm is moving to the NNW at 8kts but most models are indicating a turn towards the west shortly (see attached Early Guidance from http://euler.atmos.colostate.edu/~vigh/guidance/atlantic/early1.png again the shelf life warning applies here). 

Looking at the latest Automated Dvorak Images (Wind Table Attached) from the SSEC in Madison, WI (http://cimss.ssec.wisc.edu/tropic/adt/odt3.html) they are grading the storm as follows: CI=6.2, Minimum Central Pressure 943.1mb, and Maximum sustained winds of 119.8kt which compares with the official reading of 110kts rather well.

Given that the sea surface temperatures in the area are in the 28C range Helene should have plenty of warm water to work with over the next 24 hours or so for strengthening. (E-Wall Image http://www.meteo.psu.edu/~gadomski/SATANL_ATLSST/recent.html attached)

The Discussion from NHC makes reference to both the NOAA P3 and G4 aircraft being in the area and providing data later in the day. This would be a perfect follow up and way to practice decoding Vortex Data Messages from a real storm and good material for the upcoming Portfolio #1.

Have a great Monday, 

George

1_2006-09-18_12Z_EARLY_GUIDANCE.png    
2_2006-09-18_15Z_HELENE_WIND_TABLE.gif
 
 
3_2006-09-18_12Z_SST.gif
 

 
re: Tropical Weather Briefing #1, Week of September 18
Steve Seman - 9/18/2006 01:34 PM
Good suggestion on getting some vortex messages into the mix, George.
 
re: Tropical Weather Briefing #1, Week of September 18
GEORGE KASICA - Edited 9/18/2006 04:42 PM
Thanks, I try :)
Though it doesn't look like any messages are up on the NHC Web at this time. Is it possible they didn't send any?
 
re: Tropical Weather Briefing #1, Week of September 18
PHILIP LUTZAK - 9/18/2006 05:11 PM
Hey George,
I too have been checking online and there's still nothing out there. The 11AM discussion said that there would be an unscheduled experimental pass through Helene and now the 5PM Discussion says that a NOAA research aircraft "made a pass through the center of Helene" today, but not a full investigation. This makes me think that since it wasn't a normally scheduled run that they may never put up a vortex signature message.  In addition, if you look at the daily schedule for the Hurricane Hunters, there's nothing listed. I hope they do, but it doesn't sound promising. Oh well...
 
re: Tropical Weather Briefing #1, Week of September 18
BRANDON JONES - 9/18/2006 05:31 PM
I have been checking for the vortex messages too but haven't found anything yet. I don't know, but is it possible that only the Aircraft Reconnaissance Flights send back vortex messages to the NHC, rather than the NOAA Research Aircraft?
 
re: Tropical Weather Briefing #1, Week of September 18
LEE GRENCI - 9/18/2006 05:55 PM
As the link in Lesson 2 purports, the mission of HRD is research.

http://www.aoml.noaa.gov/hrd/overview.html

Votex messages come from data collected by the Air Force.
 
re: Tropical Weather Briefing #1, Week of September 18
PHILIP LUTZAK - Edited 9/18/2006 08:16 PM
As far as Helene’s track goes, now that she's taken the anticipated turn to the west, all of the models are getting into very good consensus on where she’s going. The early-cycle track guidance (01) shows how close all of the models have clustered; there are only 2 outliers now. You can clearly see why these models are getting into close agreement. Look at the change in the track from west to north between 48 and 72 hours, and then look at the upper right panels in these 72 hour forecasts from GFS (02) and NOGAPS (03). Notice how they have almost identical solutions, with a strong trough and cold front coming off of the east coast between the Bermuda high and the strong Canadian high to the west. The steering winds in the upper left panels show the strong south to southwest steering flow coming with the approaching trough. 
  What will be interesting to watch is Helene’s forward speed. Should she slow down any more than her current speed of 8 knots, she might miss this steering flow. Then she may be around to bother us for a longer time than we thought.
 
 
re: Tropical Weather Briefing #1, Week of September 18
GEORGE KASICA - 9/19/2006 10:23 AM
I was hoping that the P3 was the Air Force aircraft but apparently despite what the discussion stated it did not make a flight into the storm.
 
re: Tropical Weather Briefing #1, Week of September 18
WILLIAM BURNS - 9/18/2006 10:00 PM
Nice briefing George ! The GFDL seems to confirm this intensification over the 24 hours. The GFDL also shows an interesting intensity profile at 30 hrs, which caught my eye and I have attached from the 18Z run for 091806. 

The sea surface temps are above 26C in every quadrant of the storm. The westerly shear seems to be diminishing enough to allow the westward movement of Helene and the subsequent intensification.

However, I observe in the intensity panel for 30hrs, that the strongest winds (Cat 3) are on the north and west sides of the storm, which I find curious because the only shear I see on the GFS model at that time is that of the storm itself, unless the easterly shear on the southern part of Helene is not from the storm... I'm still learning so I could use some help on this one.

Unfortunately, I only have the 12Z model to go by since the 0Z model for 081906 hasn't been posted yet.
 
re: Tropical Weather Briefing #1, Week of September 18
PHILIP LUTZAK - Edited 9/19/2006 12:30 AM
Hi William,
Those are great observations and questions. From what I understand, the shear and steering can be from different directions. So a storm moving to the north with strong shear from the west will continue moving north but a lot of the convection will be blown off towards the east by the westerly shear. So it wasn't so much the west/southwesterly shear that stopped Helene from moving westward. It was the trough to her north and west, with its southwesterly steering winds, that was trying to pull her to the northeast. But at the same time there was a high pressure area building behind and north of her from the north and east. The trough was pulling her north and east, while the ridge was trying to push her westward. At first the trough was winning out, and that caused her to go north. But right now the trough is weakening, while the ridge is strengthening north of her, so she has turned westward underneath the building ridge. 
  The strong winds forecast on the north and west sides of the storm are puzzling to me too, because at that forecast time she will be moving west or northwestward. If the strongest winds are in the right front quadrant, then the strongest winds should be north and east of the center. Anybody want to comment?
 
re: Tropical Weather Briefing #1, Week of September 18
Steve Seman - 9/19/2006 12:41 AM
Remember, folks, that quadrants and sides of the storm are defined with respect to the direction of motion:

http://www.aoml.noaa.gov/hrd/tcfaq/D6.html
 
re: Tropical Weather Briefing #1, Week of September 18
WILLIAM BURNS - 9/19/2006 08:44 AM
Thanks Steve,

A key point. I missed that. So, if the storm is moving westward, the north east quadrant is the northwest side of the storm.
 
re: Tropical Weather Briefing #1, Week of September 18
LEE GRENCI - 9/19/2006 08:48 AM
In this case, I would say that the right-front quadrant (relative to an observer looking down from over the eye (or center of the storm)) lies to the north and west of the eye. Otherwise, all the directions you cited get confusing.
 
re: Tropical Weather Briefing #1, Week of September 18
WILLIAM BURNS - 9/19/2006 08:58 AM
Good point Lee, Thanks
 
re: Tropical Weather Briefing #1, Week of September 18
LEE GRENCI - 9/19/2006 09:21 AM
You're quite welcome.
 
re: Tropical Weather Briefing #1, Week of September 18
WILLIAM BURNS - 9/19/2006 08:57 AM
Hi Steve,

This may sound a little off the wall, but back in the days when we didn't have these wonderful models and you only had a surface map and an upper air map, they still had to track hurricanes and forecast their movement, right ? So, I'm curious, what quantitative measurements determined who won when it came to steering the hurricane ? In other words, if you had a hurricane with intensity x, a high pressure area to the north with pressure y, and a steering currents at 500mb to the west, moving northeast at z, how could you tell who would win in steering that hurricane or at least make a best guess ?

Bill
 
re: Tropical Weather Briefing #1, Week of September 18
Steve Seman - 9/19/2006 09:06 AM
The driving force behind steering is the wind aloft, Bill.  While steering is often explained on TV based on surface-features for simplicity of explanation, the real driving forces are aloft.  Thus, forecasters did (and still do) base forecasts on winds aloft (often the mean winds through a deep layer of the troposphere, but 500-mb serves as a proxy).
 
re: Tropical Weather Briefing #1, Week of September 18
LEE GRENCI - 9/19/2006 09:18 AM
Technically, there are two components to steering -- environmental steering currents (the mean wind in the 850-200 mb layer, on average) and the storm itself (technically referred to as the Beta effect).  You will study these components under varying conditions in Lesson 9, I believe.

The Beta effect is difficult to model, suggesting one reason for faulty track forecasts.
 
re: Tropical Weather Briefing #1, Week of September 18
WILLIAM BURNS - 9/19/2006 03:28 PM
Lee, that sounds like its going to be a very interesting part of the course. It seems like most of the track errors occur because there are no steering currents ready to pick up the hurricane yet and the movement must be due to this Beta effect, right ? Another question though, if there are no real steering currents close by to the hurricane yet, at what point does a hurricane or tropical storm's intensity totally outweigh any surface high pressure area that might be trying to steer it ?

Thanks,

Bill
 
re: Tropical Weather Briefing #1, Week of September 18
LEE GRENCI - 9/19/2006 03:47 PM
I think if we knew the "point", tracking forecasts would be dead on.  Alas, forecasting is a bit more primitive than what you might expect.  Unlike algebra, when x always =2, :-) forecasting the movement of tropical cyclones is fraught with error, particularly beyond 24 or 48 hours.  So, the answer to your question is simply ... I don't know and neither does anybody else.  If the models can't figure it out, despite computers being able to make billions of calculations each second, we humans don't have a snowball's chance in hell of saying x = .....
 
re: Tropical Weather Briefing #1, Week of September 18
WILLIAM BURNS - 9/19/2006 05:04 PM
Thanks Lee ! That just means there's a lot more to explore in the coming years in hurricane research, right ?
 
re: Tropical Weather Briefing #1, Week of September 18
LEE GRENCI - 9/20/2006 07:18 AM
Hi Bill,

Yes!  That's what I constantly tell students who frequently ask:  Why should I go into research meteorology? Easy answer: Because there are lots of outstanding problems to solve!  Cheers. Lee
 
re: Tropical Weather Briefing #1, Week of September 18
Steve Seman - 9/19/2006 03:52 PM
Bill,

This problem is not unlike what we talked about in Meteo 101 regarding the flaws of computer models.  In order to get a picture of what will happen in the atmosphere (both at the surface and aloft), we take observations (with instrument errors), and plug the data into computer models--a process called initialization.  This initialization is imperfect, too, because observations are taken at various locations that don't correspond to the geographical data-entry points for the models (grid points).  So, we start a computer model (with it's own imperfections) from and imperfect starting point.

As Lee said, various track errors are not surprising.
 
re: Tropical Weather Briefing #1, Week of September 18
WILLIAM BURNS - 9/19/2006 05:07 PM
So, that is the reason that they rely on the ensemble track forecasts ? Different initialization ? Are we going to get into the specifics of what's different with each initialization of a model ?
 
re: Tropical Weather Briefing #1, Week of September 18
Steve Seman - 9/19/2006 07:04 PM
Bill,

The specifics of ensemble forecasting are covered in Meteo 410.  In a nutshell, though, ensemble forecasts incorporate different initializations and tweaked model-physics.