A more west jog?

[cycloneye]

Is it a wobble or a trend of hurricane Frances to move this afternoon after 3 PM more west than 3 hours ago when it was more WNW to NW? After goes sat came back I see that west movement again so now let's see if it is another wobble which normally this systems do.

[charleston_hugo_veteran]

cyclone you got your supplies ready???

[x-y-no]

Yeah, it looks to have been going west from 16:15z to 19:15z. But it was going nearly NW the two hours before that. So it averages out to WNW.

[Dean4Storms]

Frances could be stair stepping, we'll have to wait and see if this trend continues.

[cycloneye]

Yes from 295-300 earlier this afternoon now it seems to be at 280-285 range.

[Air Force Met]

It's bumping up against the ridge. Ridges and trofs are rarely straight or nicely curved lines. If you (especially the mets here) have ever done micro-analysis or reanalyzed an upper level chart then you realize how much smoothing takes place by the model.

So...where the GFS (or any model) shows a nice ESE-WNW oriented ridge or contour line...in actuality it is kinda jagged. It may go west...then wnw...then nw...then back wnw...etc.

You see this a lot when a tropical cyclone is on the SW sie of a ridge...where the ridge may be a little weaker in one area and a little stronger in another.

So...its normal. WNW is the orverall track.

[PurdueWx80]

It's bumping up against the ridge. Ridges and trofs are rarely straight or nicely curved lines. If you (especially the mets here) have ever done micro-analysis or reanalyzed an upper level chart then you realize how much smoothing takes place by the model.

So...where the GFS (or any model) shows a nice ESE-WNW oriented ridge or contour line...in actuality it is kinda jagged. It may go west...then wnw...then nw...then back wnw...etc.

You see this a lot when a tropical cyclone is on the SW sie of a ridge...where the ridge may be a little weaker in one area and a little stronger in another.

So...its normal. WNW is the orverall track.

Thanks for clearing this up. I don't think a lot of people realize mesoscale noise in the large scale synoptic setting affects weather of all kinds. Maybe this will help everyone get over the "Oh my LORD, it moved 1 degree north of WNW...LOOK OUT!"

[CaluWxBill]

It's bumping up against the ridge. Ridges and trofs are rarely straight or nicely curved lines. If you (especially the mets here) have ever done micro-analysis or reanalyzed an upper level chart then you realize how much smoothing takes place by the model.

So...where the GFS (or any model) shows a nice ESE-WNW oriented ridge or contour line...in actuality it is kinda jagged. It may go west...then wnw...then nw...then back wnw...etc.

You see this a lot when a tropical cyclone is on the SW sie of a ridge...where the ridge may be a little weaker in one area and a little stronger in another.

So...its normal. WNW is the orverall track.

Good point, I think it is also good to note that sometimes convection traveling around the center, will give the appearance of changes in direction

[cycloneye]

Those are good valid points from all above.

[vbhoutex]

Thanks guys for the great explanations!! That is infinitely better than my normal "wobbles always happen with these storms"!!!!!

[Air Force Met]

Re-analysis of the upper charts is very important...especially here (in Houston) in the summer. In the northern latitudes, the need is not so great because the contours are so close together, there is not a lot of room for error.

In the tropics...the contours can be far apart...especially in the summer and you need to do some meso and micro analysis to find out exactly where your shortwaves are...since they may be hidden in the overall pattern because of smoothing and the fact they are just not that strong.

BUT...is the south...this time of year...one little shortwave can kick off some big thunderstorms and you have to reanalyze the charts to make sure there isn't one hidden in the ridge...because if there is...that can take you from partly cloudy and 10% precip to mostly cloudy and 50% thunderstorms.

All it takes in the summer is a little bit of slightly cooler are aloft and a little vorticity and BAMM! Busted forecast.

Looking at the streamlines at about 400 mb...which should be F's steering level when she gets a little stronger...a high statys to her N and NW. Don't think she is going to be in a big hurry anytime soon.

[TerryAlly]

Air Force Met,

As a hurricane, would it now be under-going eyewall changes and when that happens, aren't there times when the eye will reform at different coordinates? Against the background of your explanation earlier, when/if there is a reformation of the eye would it still be an overall WNW movement?

[rbaker]

apparently just a wobble, and if anything is going back to that 280 or 285 course, so just play with the averages. Unless you see a definate move any one direction over a period of time of 3 hrs or more , aka Charley

[Air Force Met]

Air Force Met,

As a hurricane, would it now be under-going eyewall changes and when that happens, aren't there times when the eye will reform at different coordinates? Against the background of your explanation earlier, when/if there is a reformation of the eye would it still be an overall WNW movement?

It will be undergoing various eyewall cycles. Sometimes these cycles are very slow...and intensification is slow. Sometimes they are very rapis...like Charley. We know what leads to intensification...but the forecasting of an eyewall cycle is still very difficult and we usually don't know it is going to happen until it starts.

The eyewall will reform...but it is not really in a different location. What happens is another eyewall forms outside the current one and then contracts. The inner eyewall also contracts. Strengthening (rapid) occurs until the inner eyewall collapses and the outer one takes over.

So..the only impact on movement that comes from all that the eywall wobbles...just like an out of balance tire will wobble. It still generally moves inthe same direction but because of the various intensities of the convection...it wobbles one way and then another. These are small wobbles and don't guide where the storm goes...that is still caused by the upper level winds.

[dhweather]

It's bumping up against the ridge. Ridges and trofs are rarely straight or nicely curved lines. If you (especially the mets here) have ever done micro-analysis or reanalyzed an upper level chart then you realize how much smoothing takes place by the model.

So...where the GFS (or any model) shows a nice ESE-WNW oriented ridge or contour line...in actuality it is kinda jagged. It may go west...then wnw...then nw...then back wnw...etc.

You see this a lot when a tropical cyclone is on the SW sie of a ridge...where the ridge may be a little weaker in one area and a little stronger in another.

So...its normal. WNW is the orverall track.

What? It doesn't follow the pretty straight lines drawn on teevee?

[Air Force Met]

It's bumping up against the ridge. Ridges and trofs are rarely straight or nicely curved lines. If you (especially the mets here) have ever done micro-analysis or reanalyzed an upper level chart then you realize how much smoothing takes place by the model.

So...where the GFS (or any model) shows a nice ESE-WNW oriented ridge or contour line...in actuality it is kinda jagged. It may go west...then wnw...then nw...then back wnw...etc.

You see this a lot when a tropical cyclone is on the SW sie of a ridge...where the ridge may be a little weaker in one area and a little stronger in another.

So...its normal. WNW is the orverall track.

What? It doesn't follow the pretty straight lines drawn on teevee?

Yeah...we wish