Tropical Storm Erika

[wxmeddler]

Despite the recent convective blow up, it's not going to a boon to Erika in terms of stacking the system or boosting vorticity. It looks like from IR and Martinique radar it's more of squall line type of convective system rather than the convergence based convection. Even worse, since it's moving east, and to the south of the LLC, the squall line is creating a anti-cyclonic wake to the north side.

[EasternUSWX]

Despite the recent convective blow up, it's not going to a boon to Erika in terms of stacking the system or boosting vorticity. It looks like from IR and Martinique radar it's more of squall line type of convective system rather than the convergence based convection. Even worse, since it's moving east, and to the south of the LLC, the squall line is creating a anti-cyclonic wake to the north side.

 

Disagree. Looks like starting to cover center nicely. 

 

[Superstorm93]

It has the same pattern it had this morning. Rinse and repeat.

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[SN_Lover]

Disagree. Looks like starting to cover center nicely. 

 

 

wxmeddler is right. No banding around the center, just a squall line feature. 

[EasternUSWX]

wxmeddler is right. No banding around the center, just a squall line feature. 

 

That radar is not close enough to see. Any ways what time is the next second flight?

[IsentropicLift]

The good news is that in about 24 hours the system will be passing quite close to KSJU and that will give us a rare oppertunity to see the structure of the core on quality American radar.

[Cheeznado]

The biggest question is not really intensity, but track. The really big shift right in the models says that there is a pretty good chance this will not hit the US. We will see if this trend holds with the 00Z suite.

[EasternUSWX]

The biggest question is not really intensity, but track. The really big shift right in the models says that there is a pretty good chance this will not hit the US. We will see if this trend holds with the 00Z suite.

 

Hurricane models shift more then the ground in California. I wouldn't even consider a miss till it gets past PR. 

[jojo762]

The biggest question is not really intensity, but track. The really big shift right in the models says that there is a pretty good chance this will not hit the US. We will see if this trend holds with the 00Z suite.

It did...

[HKY_WX]

I don't think the pattern really supports a recurve in this situation, although as we have seen in the past, even a slight erosion of the western ATL ridge can cause a recurve. That said, I could certainly see a situation where we see a gradual northerly bend and an eventual landfall over the NC coastline. Perhaps on a NNE course. Of course anything is still possible, but there is no large incoming trough to deflect this. 

[HKY_WX]

I have to say though, the pattern on the GFS at 129hrs is Hugo redux. With the weak upper low over the northern golf and the ridge to the north. That would favor a bend back to the WNW or NW and a strengthening scenario.

[Jackstraw]

Despite the recent convective blow up, it's not going to a boon to Erika in terms of stacking the system or boosting vorticity. It looks like from IR and Martinique radar it's more of squall line type of convective system rather than the convergence based convection. Even worse, since it's moving east, and to the south of the LLC, the squall line is creating a anti-cyclonic wake to the north side.

 

Saw a lot of out flow boundries eminating from the convection on visible today also.

[Superstorm93]

Actually getting vented pretty well 

 

[IsentropicLift]

This looks awfully familiar

 

[SN_Lover]

NAM has something off of the NC coast on the 29th. Sign of things to come? 

[Eastatlwx]

This looks awfully familiar

good thing is we have a ridge of high pressure

[IsentropicLift]

Actually getting vented pretty well 

 

Outflow has looked good most of the day. If not for the disjointed centers this thing probably would have really taken off today. Right now I think its biggest inhibitor is poor structure.

[DopplerWx]

nhc shifts a bit east.

[IsentropicLift]

good thing is we have a ridge of high pressure

This isn't January with a 1046mb high sitting over downeast Maine and a -NAO block over Greenland.

 

In other words, I think the system slows down near the Carolinas but I am not buying a sharp curve East. If anything, it should slowly side North once the high gets out of the way.

[Eastatlwx]

This isn't January with a 1046mb high sitting over downeast Maine and a -NAO block over Greenland. I agree with the part you said about it slowly sliding north as the high lifts off, but it is too far off to really know how and where it moves once the high pressure slides away

In other words, I think the system slows down near the Carolinas but I am not buying a sharp curve East. If anything, it should slowly side North once the high gets out of the way.

[DopplerWx]

little weakness in the shear showing up just ahead of erika.  will need to thread it while keeping the coc in tact.

[IsentropicLift]

Interesting how the higher res models are all sticking together. Even though the NAM is garbage for tropical forecasting, it does show a solution that matches up well with the rest of the guidance.

 

[IsentropicLift]

little weakness in the shear showing up just ahead of erika.  will need to thread it while keeping the coc in tact.

Erika needs to pass well Northeast of Puerto Rico tomorrow. 

[dtk]

I've said multiple times in this thread that global models are very useful for determining large scale steering patterns, they are an essential tool no doubt. However the actual projection of a tropical cyclone in a global model is fairly dismal. I think the false alarm rate for RI is so high that the magnitude of the low in a global model projection shouldn't really be considered. Unfortunately the GFDL and HWRF have even worse false RI rates. Likewise there are numerous times where globals show a weak cyclone or open wave and it ends up being a hurricane.

 

We can all agree intensity forecasting for TCs is terrible, and has shown almost no improvement for the 2 decades I've been watching. If you can't forecast intensity then you can't forecast the TCs effects on the upper-levels, since the strength of a TC's upper-level anti-cyclone and Rossby Wave is directly connected to intensity. This results in innacurate representation of steering currents, and this effect butterflies out. Beyond 3 days track forecasting is quite poor, I think we're at the point where we can't produce better track forecasts until we solve the intensity problem. All models have this problem, but globals are particularly bad since they cant resolve the effects on steering. At least the GFDL and HWRF have enough resolution to produce the realistic upper-level features, if they can get the intensity right. Observations is another problem that feeds back into this, and might be the key to unlocking it.

 

The only time globals are quite useful is in the case of a large, mature hurricane. With something like Erika the results are abysmal.

HWRF is starting to show steady improvement through HFIP investment over the past 5 years, see for example slide 5 of the following:

https://www.wmo.int/pages/prog/arep/wwrp/new/wwosc/documents/WWOSC_Tallapragada.pdf

 

I don't think that track forecasting is nearly as bad as you're making it out to be, and it continues to improve:

http://www.nhc.noaa.gov/verification/figs/ALtkerrtrd_noTD.jpg

 

Present day 5 day track forecasts from NHC are as good as 3 day track forecasts were 2000.  Oh, and most of their track forecasting comes from taking model consensus, so the implication there is that track forecasts in the models also continue to improve.  This disagrees with your point that you "have to get the intensity" forecasting right in order to continue to improve track forecasts. 

 

We can agree to disagree on the last point.  The skill of track forecasting by global models will vary by storm (size, intensity, steering, etc.), but I don't think you can generalize as much as you are trying to.

[bdgwx]

It did...

 

Attached Images

 

 

I can't be totally positive, but I think cheeznado was referring to the actual 00Z cycle runs. Someone correct me if I'm wrong, but I believe all of the runs listed in the 00Z model track guidance plot from TTB are based on an already completed cycle. For example, the 18Z GFS (listed as AVNI in red) is depicted with an offset of 6 hours. It's the same with the HWRF (list as HWFI in purple) and etc. It's a bit cluttered, but I couldn't find the Euro in there which is unfortunate.

[Derecho!]

Current 3-5 day TC forecast track accuracy is an astounding human achievement, IMHO. It's actually made following the tropics a little more boring for me since when I started in 1995.

[Eastatlwx]

This isn't January with a 1046mb high sitting over downeast Maine and a -NAO block over Greenland.

In other words, I think the system slows down near the Carolinas but I am not buying a sharp curve East. If anything, it should slowly side North once the high gets out of the way.

I agree with the last part, question is where does it go.

[eurojosh]

Present day 5 day track forecasts from NHC are as good as 3 day track forecasts were 2000. Oh, and most of their track forecasting comes from taking model consensus, so the implication there is that track forecasts in the models also continue to improve. This disagrees with your point that you "have to get the intensity" forecasting right in order to continue to improve track forecasts.

I'm probably the furthest thing from an expert there is in here, but I don't see how the tropical model intensity forecasts, and the global model track forecasts, are anything but codependent. I mean, how can you trust an intensity forecast without the context of a track - there's obviously a lot more than internal dynamics at play (shearing, dry air, mountains - all track dependent). And, at the same time, as intensity shapes track (see recent debate on Danny), how can you forecast track without a good model of intensity?

Bottom line - and I'm sure this is a gross oversimplification of the middle ground between TH and DTK - but don't both global and tropical models have something useful to contribute to the forecasts that Mets derive from their analyses of both?

[IsentropicLift]

The 00z GFS is much, much better through 60hrs

[dtk]

I'm probably the furthest thing from an expert there is in here, but I don't see how the tropical model intensity forecasts, and the global model track forecasts, are anything but codependent. I mean, how can you trust an intensity forecast without the context of a track - there's obviously a lot more than internal dynamics at play (shearing, dry air, mountains - all track dependent). And, at the same time, as intensity shapes track (see recent debate on Danny), how can you forecast track without a good model of intensity?

Bottom line - and I'm sure this is a gross oversimplification of the middle ground between TH and DTK - but don't both global and tropical models have something useful to contribute to the forecasts that Mets derive from their analyses of both?

 

For the most part, I largely agree with your first paragraph.  However, there are factors that contribute to track prediction that are partly or wholly external to the intensity forecast itself.  These things continue to improve through better modeling, better DA, etc.  Undoubtedly, improved intensity predictions will further accelerate our improvements in track prediction. 

 

Yes, both global and regional/tropical specific models have their place in the forecast process (as do some statistical tools, btw).  I'm not arguing the utility of regional models (they are obviously useful and worth the investment)...I'm simply trying to make the point that global models are more useful than some are opining about.