Upcoming week - September 4-9

[Andrew92]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

Evaluating last week

First off, I want to thank those who commented saying this was one of my best analyses of the year to date. I did put a lot of work into this past week. However, this analysis also turned out to be far from perfect. I think I am guilty of a major thing this past week: paralysis by analysis. Believe it or not, before I wrote this, I was ready to call Invest 97L as Kirk and a category 2 storm by the weekend coming in, but the models told me otherwise and failed me. That was the most egregious eyesore of this past week, not calling for that one to develop. That said, I did nail the type of track I thought it would take, a track out to sea, and since it also didn’t hit land unlike Isaac, the bad portion that is this storm takes a little less heat overall for the week. This is also similar to another feeling that I had with Chris and Debby early in the year. Remember when I told about that dream of Chris over the Atlantic, and Debby in the Gulf of Mexico heading to Florida, both at the same time? That scenario came to also perfection – and I didn’t listen to my gut.

Wow, I just got way ahead of myself there. Let’s look at Isaac. I was certainly right on the track up to a landfall in Louisiana, including when the final one would take place, sometime early on Wednesday morning. I also nailed the strong wave effects from the Florida Gulf Coast around to Mississippi and Louisiana, being stronger in south and central Florida, lesser further north, and then larger waves further and further west. I underestimated that these waves would also produce the type of storm surge that Isaac wound up producing though, mostly because of the angle I had Isaac making landfall at. I was about right on that northwesterly acute angle relative to the coast though. I was also pretty accurate in picking Gustav as an analog in that regard, but in doing so, I probably should have given more merit to the type of coastal flooding that could take place, and it happened in earnest. The exact landfall location was just barely east of Houma, a little outside my window, but not too far off. Isaac’s winds were also quite a bit lower than I anticipated, coming in at 80 mph officially (though 85 mph at post-analysis would not entirely surprise me either, given that it was strengthening up to landfall), but I was accurate on a pressure in the 960’s at minimum. Isaac then slowed down for a longer period of time than I thought over Louisiana, so the timing for reaching the Midwest and Great Lakes was about 24 hours off. Also off was the weakening to a tropical depression, though Isaac did weaken to a tropical storm when I thought it did; Isaac took an extra 12-18 hours to weaken to a depression. Still, I did call for a track like this, lots of inland freshwater flooding in Louisiana and Mississippi (though also in eastern Texas and Arkansas, which wasn’t quite as pronounced), and tornadoes were indeed common in the eastern bands of this storm, including in Mississippi and eastern Louisiana. I underestimated that threat to Alabama and the western Florida Panhandle though.

All told, with what I had to work with, I think I did a very decent job with Isaac. The track and timing up to landfall and even through Thursday were accurate, but Isaac did slow down more than I thought. Isaac had problems having stronger winds, but deepened to what I thought it would in terms of pressure. The track was a little east of what I thought but not too far off. Lastly, though off a little in places on the effects, these mistakes were for the most part minimal. I give myself a solid B for this storm.

As mentioned, I blew which disturbance would become Kirk. That said, the track for Invest 97L was accurate. But what about that the system I predicted to become Kirk? Well, since it was beat to that name, it was Leslie instead. For a late-week storm, which are always harder for me to predict, I didn’t do too horrible. I did underestimate the intensity, calling for a weaker 45-50 mph storm instead of the moderate to strong tropical storm she has become. Leslie (which remember I had becoming Kirk instead) also tracked further north from what I anticipated, but the reliable models did paint a picture of this storm heading pretty close to the Leeward Islands at the time. The timing of development into a tropical cyclone was impeccable, as it happened right on Thursday as I predicted, though a tropical storm came sooner than expected. The name may have been the wrong one, but the meteorology behind this system wasn’t terrible with what I had to work with. However, a tropical depression also formed today that no models saw coming, but it hasn’t gotten stronger as of yet. I don’t know that I would have called for this development with what I had to work with.

Overall, this was a pretty tough week, I did blow it with Invest 97L as it became Kirk, but what happened with the system that I thought would be Kirk instead was passable but not too great with what I had to work with. I also didn’t see the thirteenth depression coming, but that was probably a tall order and it is far out there. But the decent job I did with Isaac should really be what defines this past week. Despite not doing so out with Kirk and Leslie, the decency of the Isaac prognostication not only saves this week, but because it was the big story given what it did, it does nearly fully define it. I give myself a B- for this past week.

Leslie continues to churn, and what will this depression do? Let’s take a look.

Current situation and models

Tropical Storm Leslie is churning very slowly between the Leeward Islands and Bermuda with maximum winds of 65 mph. Some shear continues to impact this system, but she has been an overachieving fighting since her inception. That said, this shear will probably not relax until about Wednesday sometime. By then, an upper-level anticyclone may very well be present over Leslie, which is very favorable for intensification. As for the track, Leslie is charting new ground in heading northward towards Bermuda relative to this season. However, it is also moving very slowly, and not forecast to speed up more until at least Friday. This will give Leslie ample time to strengthen before reaching Bermuda on probably Saturday or Sunday. After that, the northward track should continue, maybe bending to the right somewhat, and Leslie should definitely remain off the East Coast. Right now, Leslie is predicted to peak at 100 mph, but Gordon and Kirk have already overachieved in these subtropical latitudes. I think it is very much possible that Leslie will be a major hurricane before this week is up.

The thirteenth tropical depression developed rather quickly today. However, this system does not look to be in any hurry to intensify into much. It is a very small system with very little convection near the center. These small storms are very susceptible to the slightest changes, and this depression is simply not forecast to be more than a very minimal tropical storm while churning over the open Atlantic. It is in that same area where Gordon and Kirk recently overachieved though, so a tropical storm cannot be ruled out. However, the trend from the first advisory to the second has been for this to be a tropical storm for less time than before, which is never a sign of any significant intensification taking place. Northwesterly shear is already present over this system, but probably not overly strong to prevent some slight intensification. Then again, shear is forecast to increase with the approach of a trough of low pressure arriving from the Canadian Maritime Provinces. This system is forecast to de-generate into a remnant low by Thursday, never threatening land.

Lastly, the GFS and Euro models are hinting on a tropical cyclone developing during the weekend, most strongly on Sunday. This system looks to really organize sometime on Sunday near the Cape Verde Islands. Beyond that will be for next week, but this is an intriguing feature nonetheless.

Recent history

In El Nino years since 1960, these storms have taken place during this upcoming week:

Betsy in 1965 (already active)
Carrie in 1972
Dawn in 1972
Frances in 1976 (already active)
Clara in 1977
Danielle in 1986
Cindy in 1987
Claudette in 1991
Danny in 1991
Floyd in 1993
Debby in 1994
Erika in 1997
Edouard in 2002
Fay in 2002
Gustav in 2002
Florence in 2006
Fred in 2009

That’s a total of 17 storms in 17 El Nino years since 1960, or one storm an El Nino year on average this week. Two were already active, Betsy in 1965 and Frances in 1976, but all the others were newcomers. Ten of these storms eventually became hurricanes, but not all necessarily during this week itself. Additionally, five became category 3 storms: Betsy, Frances (though earlier), Claudette, Erika, and Fred. Of these five, only Claudette did not come from a tropical wave. However, only Fred reached this intensity south of 20 degrees latitude. Fred is also the only one to become a major hurricane east of 50 degrees longitude in an El Nino year this upcoming week.

The storms that developed in the Main Development Region this upcoming week include Danielle in 1986, Cindy in 1987, Danny in 1991, Debby in 1994, Erika in 1997, Florence in 2006, and Fred in 2009. Only Erika, Florence, and Fred managed to become hurricanes of these seven storms. Debby briefly came close, but like the other three before her, struggled mightily in the tropical latitudes. Florence also didn’t become a hurricane until it was past 20 degrees latitude.

An uptick in tropical activity spawned by frontal systems is also seen during El Nino years this upcoming week, with seven such storms occurring. Four of these became hurricanes at some point, but only Claudette became a major hurricane of this mini-set. Also, only Gustav became stronger than a category 1 storm, near 40 degrees latitude but with a pressure in the mid-960’s – shortly after this upcoming week was over though.

So what does this all tell us?

Leslie came from a tropical wave. She has been a fighter against some pretty decent shear and is yet trying to intensify while moving slowly northward towards Bermuda. She is also now north of 20 degrees latitude, west of 50 degrees longitude, and the shear is forecast to lessen. This is the best chance for any storm to date in 2012 to become a category 3 or higher storm. With this storm possibly heading right to Bermuda, this island should definitely be prepared to batten down the hatches for a potentially very dangerous storm, like Fabian in 2003. It may not look too impressive right now, but Leslie should grow stronger in time.

The thirteenth tropical depression is in an area where storms have overachieved in intensity this year, and numerous other storms find ways to intensify in El Nino years. However, the cards are stacked mightily against this one. It is already battling some shear right now and sometime tomorrow that shear is only supposed to get stronger. We may muster a weak tropical storm, but no stronger most likely. I even wonder if 39 mph is pushing it with this system, given how disorganized and unhealthy it looks already.

Later in the week we could see a tropical depression or even storm form near the Cape Verde Islands. These systems are persistent this year, and a storm trying to intensify more than predicted for now should be looked at. However, there will be a lot of time to watch such an entity, and while I will likely call for a tropical cyclone of some sort, what it might do throughout its life will probably be for next week primarily, though I do have ideas with historical analogs and the pattern this year to work with.

The prediction

I’ve decided after last week and another incidence earlier this year, that even with all this data at my fingertips, I still need to go with my gut. And my gut tells me that Leslie is going to pop this week more than currently forecast. I predict that Leslie will hold her own until Wednesday morning with maximum winds of 60-70 mph. On Wednesday, Leslie will slowly start to strengthen more and become a hurricane late that night. Up to that point, Leslie’s track will be very slowly north to north-northwestward. Leslie’s slow track in that direction will continue through Friday night, with continued intensification to a category 3 hurricane on Friday morning or afternoon, with maximum winds at 115-120 mph before the day is up. On Saturday, Leslie will begin to accelerate northward and grow in size, fluctuating some in winds. On Saturday evening, she will make her closest approach to Bermuda with maximum winds in the 105-115 mph range, with hurricane force winds, high waves, and a potentially damage storm surge all possible for the island. After passing Bermuda, Leslie’s track will bend to the right, slightly north-northeast, and accelerating faster towards the Maritime Provinces as a category 2 storm with winds of 100-105 mph, still about a day away from that area. Throughout the week, Leslie will grow in size, and her somewhat close proximity to the East Coast will also produce dangerous rip currents along the coast. Confidence is 60%, but please remember not to treat this as an official forecast! Please listen to the National Hurricane Center for official forecasts, and your local authorities on what to do if this potentially dangerous storm hits your area. Thank you.

What about that depression? I predict this tropical depression will not intensify any further before de-generating into a remnant low on Wednesday. Confidence is 70%.

And will anything else come this week? It is approaching the climatological peak of the season, and with the way this season is behaving, I think we do see something. I predict a tropical depression to form near the Cape Verde Islands on Saturday night, and become Tropical Storm Michael with maximum sustained winds of 40-50 mph on Sunday. Confidence is 65%.

-Andrew92

[somethingfunny]

Great forecast and I agree on just about all of these points!

[Sanibel]

There appears to be no Atlantic ridge in place relieving Florida of concern over Cape Verde long-trackers for the time being.

[HurricaneFan]

Sounds very reasonable,but what about the Tropical Wave that is WSW of the Cape Verde Islands right now?Are conditions too hostile for it to develop?
And where do you think it will go?

[somethingfunny]

Oh Michael.

[Andrew92]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

That tropical wave west-southwest of the Cape Verdes is firing thunderstorms, but nothing seems terribly organized for the time being. On top of that, no models seem to be developing this feature at all. I think this will continue on a westward track with no further development this week.

And yeah, that depression surprised me and became Michael anyway. He also looks to be another potential overachiever in the subtropical latitudes. I guess I should have maybe thought of this, except that no models were picking up on this possibility. However, if we still get another storm on Sunday near the Cape Verdes, and its name just happens to be Nadine, the point is getting the science and meteorology of such a system as accurate as possible. Therefore, I'll still have done well in showing that it would be there - it just didn't get the name I expected it to.

I am also starting to see a reason for this level of overachievement. Sea surface temperatures from the Azores southwestward are well above normal right now. When you couple that with subtropical latitudes usually being more favorable than tropical latitudes for intensification during El Nino years... you have a strange year indeed. It's average, maybe even active. However, it is most active in these subtropical latitudes, and less so in the tropics. Or at least, that's what it looks like to my eye (pardon the slight pun).

-Andrew92

[Andrew92]

Time to get this over with and evaluate....

Ugh. That is about the only word to describe this past week’s prediction. Let’s just get this one over with.

First off, let’s dissect Leslie. I thought Leslie would become a hurricane on Wednesday, which it actually did. However, I also thought this would be the beginning of an intensifying trend; this did not exactly materialize. I thought Leslie would be a category 3 hurricane by the end of Friday! Instead, it was a tropical storm on a slight weakening trend. I did nail the early part of the prediction, with the storm moving very slowly. However, this storm tracked north even slower than forecast, and is still passing east of Bermuda as I type this. Granted, what I predicted was almost in line with the official forecast and models for the time, and there were no trends in those forecasts except maybe a slight eastward shift – but none in intensity. If anything, the trend for storms in these temperate latitudes has been to overachieve, leading me to go along with that line of thinking with this storm.

As for that depression, as it was at the time, this was a catastrophe for me. It is at least way out over open waters and not affecting anybody, but still this thing became a lot more than what I thought. I thought this would dissipate by Wednesday, and it instead is still around as a persistent hurricane. On the other hand, I had a prediction that the first major hurricane would form during this week and that was certainly right; just with the wrong storm.

To top it off, I predicted another storm to form off the African coast during the weekend. There is an Invest, but no tropical depression or storm for now. Getting the name wrong would have only signified getting something else wrong – had a storm developed here when I thought and been named Nadine, I would have gotten the science right, and thus would have done well there, in case you are wondering. But since nothing developed, I didn’t do so well.

At least nothing else developed this past week. But meh, I am ready to move forward from a near completely blown prediction. I’ve done fairly well up to this point, and even my worst weeks up to now have still passed, but not this one. I give myself an F for this past week – and it was a quite spectacular one at that.

New week coming up soon. Hopefully I can do a little better.

-Andrew92