Upcoming week - September 17-23

[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

This past week started out with Leslie and Michael, and now ends with Nadine. Predicting the dissipations of Leslie and Michael were both pretty easy, as well as the timing of both them happening on Tuesday. Leslie did pose a slight challenge in that intensification did occur up to landfall in Newfoundland on Tuesday. However, I thought it might sneak in and become a hurricane, but it wound up coming just short at 70 mph. Regardless, the effects of Leslie were still likely the same as it would have been as a hurricane, with mostly heavy rains and some surf, but lesser wind effects. Damage on Newfoundland appears to have been minimal from that storm.

But then Nadine came. Fortunately, I predicted the tropical depression to form on Tuesday, which happened. It became a tropical storm late on Tuesday, a bit earlier than I predicted as I did so for Wednesday. This storm then also got stronger than I thought as it first developed; becoming nearly a hurricane late on Wednesday, when I thought it might struggle with winds of 45-60 mph around that time. However, her strengthening stalled until Friday, when she finally decided to become a hurricane – by this time I thought she would be a category 2 storm though. I also thought she might sneak in and become a major hurricane on Saturday by passing over a tongue of warm waters, but it didn’t happen. A weakening trend has started on Sunday though, which is when I expected this to occur. As for the track, Nadine did pass 20 degrees latitude a bit further east than I thought and on Tuesday instead of Thursday, but reach its farthest west at 54 degrees – I had said it would re-curve very near 55 degrees, so this was about close enough. However, I thought it would be west of the Azores by this time too, and I guess it kind of is. My point though is that I thought it might be further north, and heading northeast instead of due east by now.

Overall, Nadine was a quite tricky storm to forecast. I had most of the track down, and the timing of development. I even saw a time of stagnant intensification over a period of a couple days, but the timing was 24 hours off and this storm was nearly a hurricane by that time. Nadine also didn’t grow nearly as intense as I thought. However, all things considered, I did a pretty passable job on this storm. Coupled with timing Leslie and Michael’s dissipations accurately, and correctly not calling for any other tropical storms to occur, I give myself a B- for this past week.

Needless to say, I did far better than the week before. Let’s do even better yet this week!

Current situation and models

Nadine has just weakened to a tropical storm out over the subtropical Atlantic Ocean. She is moving quickly eastward, but forecast to turn more to the northeast over the next couple days while weakening to a tropical storm probably on Monday. This is primarily due to a shearing environment that this storm has been caught in for much of its life. However, that environment may cease by about Wednesday – but in its place, waters may become cooler and the atmosphere may become drier and more stable. I’m not so sure that these factors will weaken Nadine much as she slowly nears the Azores by Friday, but she shouldn’t strengthen at all either. As Nadine reaches the Azores, she could also interact with another nearby mid- to upper-level low to the northeast, causing her to turn more eastward while moving slowly near the islands. After this happens, the GFS and Euro actually show a looping motion back towards the southwest, possibly in response to a developing ridge of high pressure. The GFS shows a weaker system, but the Euro latches onto a rather well-organized, potentially still strong tropical storm in that area.

A tropical disturbance approaching the Lesser Antilles, Invest 92L, is being monitored for tropical development. Conditions are not currently favorable for development, but the National Hurricane Center suggests they could become more favorable by the middle of the week or so. However, neither the GFS or Euro suggest any development out of this system this upcoming week as it traverses the Caribbean, likely due to some wind shear and dry air in this area.

Another disturbance in the northwestern Gulf of Mexico, Invest 93L, is showing potential signs of tropical or subtropical development as well. This system is heading northeast at 10-15 mph, and as such may not have a whole lot of time to develop into much, if anything. The GFS and Euro both show this system heading straight into Louisiana likely on Monday, and then being absorbed into a front shortly after that. Neither shows any further development of this system.

The GFS seems to pick up on a tropical wave trying to develop near the Cape Verde Islands by Friday or so and getting stronger over the weekend. The model shows a northwestward to northward track for this system after doing so. The Euro also sees this system, but is showing no development for now. Until I see other models showing this developing, I will likely not call for a tropical depression to develop in this part of the world for the weekend.

It should also be noted that, due to the Euro showing a less favorable MJO, and stronger shear taking place for the rest of the month, that Dr. Gray and Dr. Klotzbach at Colorado State University have also predicted a below average period up until September 27. They contribute this to Nadine still being active over the Atlantic, but conditions otherwise being too stable and unfavorable for much else to take place, if anything.

Recent history

In El Nino years during this upcoming week since 1960, these storms have developed or been active coming in:

Carol in 1965
Subtropical Storm Charlie in 1972
Debby in 1982 (already active)
Earl in 1986 (already active)
Dennis in 1987 (already active)
Emily in 1987
Bonnie in 1992 (already active)
Charley in 1992
Danielle in 1992
Gert in 1993 (already active)
Harvey in 1993
Ernesto in 1994
Isidore in 2002
Josephine in 2002
Kyle in 2002
Lili in 2002
Gordon in 2006 (already active)
Helene in 2006 (already active)

That’s a total of 18 storms this upcoming week, with Nadine about to make it 19, or about one every El Nino year on average. However, note that three storms occurred in 1992, all in the subtropics. Also, four storms occurred in 2002, two in the tropics and two in the subtropics (with one lasting a mere 48 hours). 12 of these storms became hurricanes, with six going on to become category 3 or higher at some point in their lives – whether previously, during this week, or later. However, only three storms – Carol in 1965, Emily in 1987, and Helene in 2006 – became hurricanes very near or south of 20 degrees latitude. Emily even briefly became a category 3 hurricane south of that latitude. This is despite 11 of these storms taking place from tropical waves, not frontal systems.

The storms in the far east Atlantic and over subtropical waters this upcoming week included Carol in 1965, Bonnie and Charley in 1992, Harvey in 1993, Josephine in 2002, and Gordon and Helene in 2006. All of these storms except Josephine were hurricanes at some point. Also, Carol, Bonnie, and Charley made some slow, erratic tracks on their ways out to sea near the Azores. Kyle in 2002 also made a similar erratic loop west of this area, en route to a long, erratic track across the subtropical Atlantic.

So what does this all tell us?

Nadine may be appearing to head out to sea, but she may not just go out quietly. For one thing, by Friday, she should be at or near the Azores. Beyond then, the reliable GFS and Euro models show an erratic looping motion back to the southwest in this area. Four other storms have done this in El Nino years, so absolutely Nadine could do this again, though likely as a weaker tropical storm.

Invests 92L and 93L appear to have their work cut out for them to develop. Conditions are just too dry and unfavorable ahead of 92L, and 93L is forming a bit too close to land and a frontal system as well. I just don’t see much potential in either of these systems to do anything, as do the GFS and Euro models. As for the system that could take place by the weekend, again, with an unfavorable MJO perhaps taking place and conditions generally being unfavorable across the tropics to begin with, I am skeptical of this proposed activity taking place too. Such developments have happened before, but usually are weak until reaching more favorable subtropical latitudes. Even if this one does so, the air is just getting to be too stable for such a system to sustain itself.

The prediction

The tropics do appear to at least be approaching a lull this upcoming week. The one thing though is that in order to reach that lull, we have to get rid of Nadine. That will probably be too tall of a task this upcoming week, as I think Nadine may quickly become the “annoying” storm of the year. I predict Nadine will turn east-northeast on Monday. That motion will become northeasterly on Tuesday, and a slowing in forward speed will commence later on Wednesday. Nadine will weaken some up until Friday, as she nears the Azores and then begins slowing down markedly in forward speed, but still have maximum winds of 50-65 mph during this whole time. I think Nadine will pass close enough to the Azores to produce some heavy rains and possibly some isolated tropical storm force winds. On Saturday, Nadine will then begin turning south and southwestward will looping erratically through Sunday. Maximum winds will drop to 45-50 mph during this time. Nadine will still be a tropical storm by the end of the week. Confidence is 60%.

Elsewhere, I predict no development for Invest 92L, Invest 93L, any tropical system off Africa near the weekend, or anywhere else this upcoming week. Confidence is 80%.

-Andrew92

[Andrew92]

Time to evaluate!

This past week centered mainly on what Nadine would do. One thing I can say outright is that I definitely had a good feel for the track and intensity overall of what this storm would do. This storm followed a general northeastward and slowish path that grew slower as she neared the Azores. After reaching a point just south of those islands, Nadine did indeed move very erratically late in the week, though not quite in the kind of motion I had in mind. I was kind of thinking a “cleaner” loop that the jagged one she appears to be taking. I also pegged the intensity mostly correct too, keeping Nadine in a window of winds of 50-65 mph. However, I did think Nadine might weaken during the weekend, and that didn’t really happen. I say that because Nadine did briefly become extratropical, only to become tropical again, and then began to strengthen again on Sunday. Then again, I don’t know that I would have had any way of predicting that kind of evolution late in the week like that. The fact remains too that I also thought Nadine would still be a tropical storm by this time, a gutsy call to make for a storm in this location on a track like this. Overall, I did a very decent job predicting what I thought Nadine would do.

Finally, I also correctly predicted no other tropical cyclones would develop during this past week. One disturbance came very close in the middle to late part of the week near Bermuda that I didn’t see, but it didn’t develop either. Altogether, I give myself an A- for this past week.

New week (again featuring Nadine, pulling my hair out following her!) coming up shortly.

-Andrew92