Looking Down the Road

[Anonymous]

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IWIC Atlantic Tropical Weather Discussion - 24 June 2004 - 8:20 PM EDT

Shower and thunderstorm activity in the northwest Gulf of Mexico is associated with tropical moisture being drawn northward into a land boundary over the southeast by the Atlantic ridge. Tropical development will not occur. The remainder of the Atlantic Basin is still very quiet. Upper level lows enhancing strong westerly shear is controlling much of the weather in the Caribbean in western Atlantic.

As stated yesterday evening, the potential for a named storm forming during the last few days of June look very slim at this point. Our seasonal hurricane forecast released on May 25 called for no June storms, so this is a good way to start the season. Now we begin to look forward into the month of July. We're forecasting 1-2 tropical storms to form next month. None of which are expected to reach hurricane status. The primary area we're going to focus on is the Mean Development Region (the area between the Lesser Antilles and the coast of Africa). The runner-up region is the western Atlantic. The 384H GFS forecasts often change numerous times, but these runs are somewhat useful for getting the general idea of what we might expect over the next couple weeks. The GFS does indicate that a series of waves will exit Africa, with the last one shown on the run being the strongest, 1010MB. Now if this were August, it probably wouldn't be anything special. However, the North Atlantic Oscillation is expected to return to neutral during that timeframe after going positive during the first week of July. The likelyhood of tropical development is slightly greater when the NAO is negative as the subtropical ridge weakens a bit. In addition, the western edge of the negative phase of the MJO will likely still be over the central/eastern Atlantic by that timeframe. But remember, we're looking as far out as July 10th, so we have a lot of time to go over model runs and TC parameters before we suggest that anything has even a 50/50 shot at development. But being that the MDR will be a place to watch next month we wanted to at least mention it.

[hurricanetrack]

I like that you too look at those long range GFS runs. I like to watch the surface, 500mb and 200mb maps to see what the pattern looks like. I've noticed more and more 594 height lines showing up lately- with some coming off of Africa. That's just like looking at more contour lines on a topo map- except that this is the atmosphere. So I guess that we are finally starting to see deeper mid-level ridging out in the Atlantic.

I also noticed the tropical waves at the end of the 18Z GFS run. Once we get past July 4th- it will be interesting to see how things pan out. Bertha in 1996 was a TD on July 4th if memory serves. Perhaps we can repeat that feat- if not by just a few days. It's getting hard to be creative with my daily commentary when it's as slow as it is right now. But- as they say, "be careful what you wish for".

[Stormsfury]

I definitely like to look at the ensembles that far out for pattern only ... which, yes, as stated above, gives some indication of what kind of pattern is progged ...

SF

[Steve H.]

Its still showing that pattern on the 6z run with ridging over the Atlantic and the low you mentioned about 1000 miles east of the islands. Not overly strong high pressure, but two domes; the Azores/Bermuda setup, with the Bermuda a bit further south than usual. Long way out, but its the pattern that looks encouraging for development signals. Cheers!!

[Anonymous]

Its still showing that pattern on the 6z run with ridging over the Atlantic and the low you mentioned about 1000 miles east of the islands. Not overly strong high pressure, but two domes; the Azores/Bermuda setup, with the Bermuda a bit further south than usual. Long way out, but its the pattern that looks encouraging for development signals. Cheers!!

Exactly...small scale atmospheric features will likely look very different from run to run. But if we truly are going into a transitional phase it should be consistently evident in model runs. This evening's GFS run continues to show the wave train, with a 1009MB low associated with a TW at 336H before running into moderate upper level winds.

[cycloneye]

Guys anything new from the models not only the GFS looking ahead for the next 10 days?

[Anonymous]

Cycloneye, the GFS is the only dependable model for the tropics that has runs extending for more than a week. Looking at the most recent few runs from today...still showing signs of a transition after July 10. What's most noticeable is that it develops a 1010MB low near 10ºN/40ºW on Day 13 and maintains it for the next 3-4 days. Doesn't strengthen it much but when we're looking this far out that's not as important as just having a persistent low in the first place. Though I imagine it would have a fairly favorable environment for the time being as the model also shows an anticyclone aloft that moves in tandem with the low...which would help counter any westerly shear that may be present. Track-wise, the GFS takes it on a general WNW course and places it near 25ºN/60ºW on Day 16.

Now I do want to stress that it's not as much as the low itself to pay attention to...but the overall pattern. Yes, the GFS is latching onto one particular wave...but it's so far out that it might as well be a different wave that develops. The point we're trying to make is...we're seeing signs that conditions in the Atlantic will change in the middle third of the upcoming month. The slow moving negative MJO currently over the WPAC should make it to the Atlantic by that time...which alone will help ripen the basin up. This and the fact that the GFS has consistently been indicating something is enough to raise an eyebrow.

It'd be foolish to actually forecast development this early in time...but it IS something to watch.

[Rainband]

Thanks for the info Rob. The GFS is good for something after all

[cycloneye]

Cycloneye, the GFS is the only dependable model for the tropics that has runs extending for more than a week. Looking at the most recent few runs from today...still showing signs of a transition after July 10. What's most noticeable is that it develops a 1010MB low near 40ºN/10ºW on Day 13 and maintains it for the next 3-4 days. Doesn't strengthen it much but when we're looking this far out that's not as important as just having a persistent low in the first place. Though I imagine it would have a fairly favorable environment for the time being as the model also shows an anticyclone aloft that moves in tandem with the low...which would help counter any westerly shear that may be present. Track-wise, the GFS takes it on a general WNW course and places it near 25ºN/60ºW on Day 16.

Now I do want to stress that it's not as much as the low itself to pay attention to...but the overall pattern. Yes, the GFS is latching onto one particular wave...but it's so far out that it might as well be a different wave that develops. The point we're trying to make is...we're seeing signs that conditions in the Atlantic will change in the middle third of the upcoming month. The slow moving negative MJO currently over the WPAC should make it to the Atlantic by that time...which alone will help ripen the basin up. This and the fact that the GFS has consistently been indicating something is enough to raise an eyebrow.

It'd be foolish to actually forecast development this early in time...but it IS something to watch.

Rob that position you posted is 10n-40 w instead of 40n-10w right?Thanks for the information and I will be watching.

[Anonymous]

You're right Cyc, my bad...fixed.

[MGC]

I also forecast no June storms. Considering the current pattern of weak fronts, I hedging my bet on a TC forming off the SE Atlantic coast next month. Doubt there is much action in Tropical Atlantic as UL winds are still to brisk. Things should start improving towards mid month.....MGC