ATL: TROPICAL STORM BILL (03L)

[Emmett_Brown]

Bill has accelerated quite a bit, 17kts, (which is 19.5 mph), and judging from the latest IR, might still be accelerating. The reason that I am pointing this out, is that Ana also flew quickly across, approaching 25 mph. Seems that trade winds are pretty strong. The result was a weaker Ana, and a busted track forecast (remember yesterday morning when Ana was supposed to hit the EC of FL?). Anyway, it will be interesting to see if Bill catches this same train and shoots past the first weakness forecast to be around 60W in 48-72 hours. For this reason, islanders should be watching just in case...

[The Eye Wall]

Wow, this storm is amazingly big and getting strong, fast. Cloud tops, per NHC, are running -80 C (-112 degrees Fahrenheit) in the CDO! That's a bit chilly.

[cpdaman]

emmit brown i think that is a great idea for islanders to still pay attention

it's nice for the models to trend away .....but stay watchful.......

which level in the steering flow Will BIll be getting steered by in the coming days

http://cimss.ssec.wisc.edu/tropic/real- ... 8dlm2.html

500-850 ......200/700 basically what level will show the weakness that will effect bill best

[AtlanticWind]

Bill is really booking . it looks like a little more westerly last few hours...

[paintplaye]

Bill is really booking . it looks like a little more westerly last few hours...

Yea it seems to be stair climbing. It will go west some then north then west then north....

[sponger]

Looking at ir i think its likely Bill is at hurricane strength. Should be a good swell producer for the east coast if he slows down on approach.

[MWatkins]

I just looked at the latest satellite loop, and I haven't seen Bill since this afternoon.

It sure does look like it is left of the NHC track for now. It might be one of these stairsteps, but the fact that it is moving faster in the forecast with the low level flow is important. They have been too slow with Ana's track and perhaps the models are underrepresenting the strenght of the high to the north.

GFS about to start coming in, will be interesting to see what it shows.

MW

[Evil Jeremy]

perhaps the models are underrepresenting the strenght of the high to the north.

That reminds me of some storm from last year. Really though, in order to make the next couple of forecast points, Bill would need to start making a bigger turn to the north over the next 12-18 hours I think. Lets see if that happens. The models had trouble with the speed of Bill days ago, perhaps that is still happening. It will be interesting to see the impact of Bill's speeding up will have on its future path.

[MWatkins]

perhaps the models are underrepresenting the strenght of the high to the north.

That reminds me of some storm from last year. Really though, in order to make the next couple of forecast points, Bill would need to start making a bigger turn to the north over the next 12-18 hours I think. Lets see if that happens. The models had trouble with the speed of Bill days ago, perhaps that is still happening. It will be interesting to see the impact of Bill's speeding up will have on its future path.

I think a benchmark to watch for is 20N 60W. If Bill crosses 20N before 60W, it's going to turn out. It it can run a degree or two south of that, it could have a chance of turning a day or two later. Although, the 0Z GFS coming in still wants to take out the ridge, but it's harder to see the specific feature that weakens the 588 ridge in the early period.

MW

[BigA]

As I head for bed, two things stick out at me about soon to be hurricane Bill. One is that Bill is getting stronger fairly rapidly. The lastest infrared loops show what looks to be a nascent eye forming in the center of the CDO. For all the nitty gritty math involved in forecasting hurricanes, and the tragedy of their devastation, there is something beautiful about an intensifying storm far away from any land.

The second thing is that Bill is hauling westward, definitely to the left of the forecast track. Whether this is a jog or a trend may be confirmed tomorrow, but as the above commenters have said, the northern lesser antilles should not let their guard down yet.

[Brent]

WOW. Remember the lack of any deep convection 36 hours ago?

[cycloneye]

the northern lesser antilles should not let their guard down yet.

Yes,until it clears the latitud of the most northern islands that is 18.6N we have to keep watching how is Bill tracking.

[Blown Away]

Looks just N of due W to me and S of the track.

[btangy]

I think a benchmark to watch for is 20N 60W. If Bill crosses 20N before 60W, it's going to turn out. It it can run a degree or two south of that, it could have a chance of turning a day or two later. Although, the 0Z GFS coming in still wants to take out the ridge, but it's harder to see the specific feature that weakens the 588 ridge in the early period.

After looking over some tropopause maps, it appears the initial weakness comes from anti-cyclonic wave breaking which allows some lower geopotential heights (or high potential vorticity) to spill in underneath the ridge. The reflection is mainly at upper levels (above 500mb). I think this is being handled pretty well by all the models as it's a pretty large scale feature with the upstream feature sampled by the radiosonde network over N America currently.

[Viper54r]

Hmm, is that a little SW jog in that last frame?

[Evil Jeremy]

Bill looks like he is going to speed past his next forecast point faster than, well, forecasted. And he also looks like he will past south of the point as well.

[MWatkins]

I think a benchmark to watch for is 20N 60W. If Bill crosses 20N before 60W, it's going to turn out. It it can run a degree or two south of that, it could have a chance of turning a day or two later. Although, the 0Z GFS coming in still wants to take out the ridge, but it's harder to see the specific feature that weakens the 588 ridge in the early period.

After looking over some tropopause maps, it appears the initial weakness comes from anti-cyclonic wave breaking which allows some lower geopotential heights (or high potential vorticity) to spill in underneath the ridge. The reflection is mainly at upper levels (above 500mb). I think this is being handled pretty well by all the models as it's a pretty large scale feature with the upstream feature sampled by the radiosonde network over N America currently.

It's hard to argue with your analysis! If I understand correctly, it sounds like, quite simply, that this is the first of two shots to the ridge. The impulse you descibe is more like additional detail on the initial breakdown of the ridge followed by the trough that finishes the job.

The only caveat left would be the underlying impact of the first shot to the ridge. If the ridge is stronger than expected and responisble for driving Bill left of track, perhaps the first round of wave breaking may not be as effective as modeled? It didn't seem as impactful in the 0Z run, which still seemed slow and right compared to the current short term motion.

Thanks again, by the way. Always appreciate your comments. Good to see you posting!

MW

[Derek Ortt]

I don't think this is moving to the west of the forecast track. That is just the convection rotating SW of the center

[thetruesms]

Mike, where do these models get info about the environment from? Are they getting it from aircraft observations or what?

Models now assimilate data from all kinds of platforms - radiosondes, aircraft, satellite, radar, dropsondes, you name it. What each specific model ingests differs from model to model. Off the top of my head, I can't recall what the specifics are, but there is plenty of documentation available. There is a whole field simply dedicated to numerical model data assimilation. Not my cup of tea, but it's very important - especially in the tropics, where determining how to deal with sometimes conflicting information, and very little in situ measurement, is common.

[MWatkins]

Mike, where do these models get info about the environment from? Are they getting it from aircraft observations or what?

Models now assimilate data from all kinds of platforms - radiosondes, aircraft, satellite, radar, dropsondes, you name it. What each specific model ingests differs from model to model. Off the top of my head, I can't recall what the specifics are, but there is plenty of documentation available. There is a whole field simply dedicated to numerical model data assimilation. Not my cup of tea, but it's very important - especially in the tropics, where determining how to deal with sometimes conflicting information, and very little in situ measurement, is common.

This is a great description. Essentially, anywhere and everywhere they can.

I know for a fact that the GFS assimilates satellite data and ship, aircraft and bouy reports. After it caught on fire when it was running on a Cray several years ago, the GFS was running on one of the fastest computers in the world. Not sure if it still is, I havent been keeping up.

MW