Upcoming week - September 10-16

[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

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.

Here is the good news: I guess I can’t do any worse, right? Let’s take a look at a brand new week.

Current situation and models

Leslie continues to hang around, now passing northeast of Bermuda with maximum winds of 60 mph. It is forecast to continue north to northeast before becoming extratropical sometime on Tuesday. However, it might not do so before reaching Newfoundland, and it could try to intensify as it speeds up. This storm lacks an inner core due to the cooler waters it churned up and then sat over for days, so that will help keep intensity at bay. Also dragging the intensity will be that it will pass over cooler waters in time. Still, Newfoundland should probably prepare for a nasty storm in the next couple days, lest it get a repeat of Igor a couple years ago – a storm that comes to mind when thinking of surprisingly strengthening hurricanes in this part of the world.

Michael was quite a surprise this past week, but is on the way down now, with maximum winds of 85 mph as it continues somewhat erratically over open waters, well away from land. One thing I did notice this past week that may have helped it to strengthen was a tongue of warmer than average waters from the Azores southwestward. It appears this storm passed over that tongue. However, it has left that anomaly, and is weakening at a faster rate and will also probably become extratropical on Tuesday or Wednesday. It should weaken to a tropical storm before doing so however, probably late Monday night or Tuesday morning.

Invest 91L is also churning west of the Cape Verde Islands. Conditions are generally favorable for development, but dry air also abounds near this system. Then again, as long as the season is a typical El Nino one and systems are south of 20 degrees latitude, systems like this tend to struggle a bit. This system will probably continue west-northwest and then re-curve north, well east of 60 degrees longitude. The trend for storms following tracks like that this year is to wait to develop until they are further north, and then overachieve from there. See Gordon, Kirk, and now Michael as recent examples. Of course, Leslie underachieved while following a similar track, but did also stall over its own churned-up waters. The other three did not do that, and no reliable model thinks Invest 91L will do the same. That tongue extending southwestward from the Azores is also hard to ignore, if all else remains favorable – and even it conditions aren’t fully ideal, they can strengthen, as Michael just did. As for intensity, both the GFS and Euro models suggest a system that struggles to intensify until sometime on Thursday, and then begins to ramp up a bit more from there. Both models seem to suggest a hurricane during the weekend while heading northeast until the weakness created by Leslie. The GFS thinks this will stay away from the land, but the Euro has this storm hitting the Azores on Sunday – potentially passing right over that tongue of warmer waters.

Nothing else appears imminent this upcoming week per any of the reliable models. There could be an interesting feature coming off Africa on Sunday per the GFS, but it will likely need time to develop initially.

Recent history

Storms that have occurred during El Nino years this upcoming week have included:

Betsy in 1965 (already active and about to make its final landfall early on September 10)
Dawn in 1972 (already active)
A subtropical storm in 1976
Clara in 1977 (already active)
Chris in 1982
Debby in 1982
Chantal in 1983
Dennis in 1987
Floyd in 1993 (already active and about to become extratropical)
Gert in 1993
Erika in 1997 (already active)
Gustav in 2002 (already active)
Hanna in 2002
Florence in 2006 (already active)
Gordon in 2006
Helene in 2006
Fred in 2009 (already active)

That is 17 storms this upcoming week that have been active or about to develop – and we will be adding Leslie and Michael to this set after this year. But we see only nine new developments, in 17 El Nino years since 1960, or about one every two such years. Only two of these developed in the Main Development Region: both of the 2006 storms, Gordon and Helene. They also eventually became major hurricanes while re-curving north east of 60 degrees latitude. The only other newly-developed storm for this upcoming week to eventually become a major hurricane was Debby in 1982. Like so many weeks that we have seen, these storms reached their peak intensities north of 20 degrees latitude. However, Helene did become a hurricane slightly south of there, in 2006.

The other storms that were hurricanes at all this upcoming week were Betsy in 1965 (which was about to make landfall in Louisiana anyway), Chantal in 1983, Floyd in 1993 (about 24 hours from becoming extratropical), Gert in 1993, Erika in 1997 (previously a major hurricane), Gustav in 2002, Florence in 2006, and Fred in 2009 (which had just weakened from a category 3 storm). Again, these storms primarily intensified in the more temperate latitudes. Only Erika and Fred became hurricanes south of 20 degrees latitude of this set – with Fred having been a major hurricane even in that area, not a common feat in an El Nino year. Of these storms, only Betsy and Gert made it further west and hit land other than the Azores, Bermuda, or the Canadian Maritime Provinces, because they also formed further west.

So what does this all tell us?

Well for one thing, by this time in a typical El Nino year, if we have an active storm in a position like where Leslie and Michael are right now, they are usually very close to leaving the picture for good. That said, Leslie may try to go out with a bang by smacking Newfoundland on its way northward. If it speeds up enough, it might be able to intensify a little before reaching there, like Igor did just two years ago. Igor was barely a hurricane poised to maybe weaken a little more before becoming extratropical, but it strengthened because it sped up some while holding itself together. On the other hand, Michael has been tenacious, but appears to be weakening at a steadier rate now. No model keeps this storm alive past Wednesday either, and it also should not hit the Azores or any land area before becoming extratropical.

However, Invest 91L will be an interesting feature to watch this week. It probably will re-curve into the same weakness carved by Leslie, but slightly further east. This system will then head out faster than Leslie has so far, and this may allow it to pass over that warm anomaly extending southwest from the Azores and become a pretty significant hurricane. The Euro takes this system over the Azores as a pretty strong system on Sunday. That said, that is a long time to prepare for such a storm, and the GFS has been pretty accurate this year. Remember, that model takes this system well west of those islands and hitting nobody.

The prediction

Nothing is ever simple in the tropics, even with systems like Leslie and Michael that are on their way out and will probably be out of the picture very soon. But I think these storms truly will be gone soon. First, Leslie: I think Leslie will gradually speed up on Monday as it continues north-northeast and reach Newfoundland on Tuesday. This faster rate of speed will allow this storm’s winds to pick up and it will reach hurricane strength again just before reaching Newfoundland, with maximum winds of 75-80 mph at landfall. Heavy rainfall, potentially damaging, will be the primary effect, along with some very high waves. Wind damage may occur, but at a lesser rate. Leslie will then become extratropical late that night as it heads away from that island. Confidence is 70%, but residents of Newfoundland, please remember that this is not an official forecast! Listen to the National Hurricane Center for official forecasts and your authorities for what to do if this storm hits your area. Thank you.

Now Michael: I predict Michael will gradually weaken to a tropical storm on Monday night as it turns back to the northwest slowly. On Tuesday, it will speed up a fair amount before becoming extratropical that evening, a safe distance between Newfoundland and the Azores. Confidence is 80%.

And then there is Invest 91L. This system may struggle for a few days, but as it re-curves, be ready to watch another beauty to behold. I predict that this system will become a tropical depression on Tuesday as it heads west-northwest over the tropical Atlantic. This system will struggle, but become a Tropical Storm Nadine on Wednesday. Intensity will stay in the 45-60 mph range until it passes 20 degrees latitude on Thursday, very near 55 degrees longitude. From there, this storm will turn north and northeast and intensify in earnest coming into the weekend. I predict a category 2 hurricane on Friday and a category 3 hurricane on Saturday with winds reaching 115-125 mph, passing over that tongue of warmer waters. On Sunday, it will begin to pass over cooler waters and weaken, west of the Azores, and have maximum winds of 85-100 mph by the end of Sunday. Confidence is 55%, lowered due to a longer-range prediction and the prospect of maybe hitting the Azores. If you live on the Azores, please remember that this is not an official forecast and to listen to the National Hurricane Center for official forecasts and your authorities for what to do if a hurricane heads in your direction. Thank you.

Elsewhere, I predict no tropical cyclone activity this upcoming week. Confidence is 90%.

-Andrew92

[Sanibel]

This is a weird season. There's dry spring-like air over us here in south Florida at the peak of the season. I think this same air has choked-off formation all year.

Normally I would say look to the Caribbean with this ridge-less north-heading pattern, however that airmass seems to be a permanent feature as part of some kind of Nino year.

We'll see what October holds.

[Andrew92]

And it's time to evaluate, with the latest advisory on Nadine in.

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.

New week coming up shortly.

-Andrew92