Small disturbance spinning near 25N 67W

[ozonepete]

While a vigorous wave pushes on directly over the big islands from Puerto Rico to Hispaniola under punishing shear, I just wanted to point out the small disturbance north of there around 25N and 66W. It has no low level vorticity/spin but is spinning very clearly at mid-levels on the satellite loops; that spin shows up at 700 and 500 mb on CIMSS. The reason I'm pointing it out is that it's sitting over very warm water and in a low shear environment, and since there are no steering currents there and won't be for a few days (a big Bermuda high is building over it), it will remain stationary and continue to spin in that area for the next few days, which gives it a chance to develop. Just something to watch.



700mb vorticity:


500mb vorticity:


shear values:


steering currents:

[TropicalAnalystwx13]

It's under an upper-level low and has no convergence/divergence. Doubt anything comes from it.

[floridasun78]

if move were will it go?

[ozonepete]

It's under an upper-level low and has no convergence/divergence. Doubt anything comes from it.

I wouldn't give it even 50/50 today, but that wasn't my point. Any persistent cluster of convection/thunderstorms over very warm water that is not forecast to move much for a few days becomes an area of interest, regardless of whether it has good upper level divergence or lower convergence. Also, many upper and/or mid-level lows get cutoff from the flow in dead steering areas such as this and gradually work their way down to the surface. As they do the upper level winds die out but the mid-level spin maintains itself due to the strong surface convergence and rising currents from clustering thunderstorms. It is one of the most common ways to get a TC in this area that does not result from an easterly wave.

P.S. The upper low is already very weakened. Look at the upper level winds at 200 and 300mb (not the shear of course which are layer averages.)

[ozonepete]

if move were will it go?

Can't tell because it would have to develop first (and reach a certain level in the atmosphere) before we could use forecast steering currents to see where it would go. But for the next few days at least the steering winds will remain dead there so it's not going anywhere.

[floridasun78]

if move were will it go?

Can't tell because it would have to develop first (and reach a certain level in the atmosphere) before we could use forecast steering currents to see where it would go. But for the next few days at least the steering winds will remain dead there so it's not going anywhere.

ok ty ( i notice that area too put their almost dont form if upper low)

[gatorcane]

There is alot of dry air just off to the west over the Bahamas that is getting sucked into this small disturbance looking at the WV loops tonight. I am guessing that because of this dry air it is losing convection. I guess if it sits there an spins for several days over warm water, you never know, but with zero model support and little convection, I don't think anything comes of this system.

[StormTracker]

You never know OP! If something does ever become of this, you got 1st dibs on it!

[ozonepete]

There is alot of dry air just off to the west over the Bahamas that is getting sucked into this small disturbance looking at the WV loops tonight. I am guessing that because of this dry air it is losing convection. I guess if it sits there an spins for several days over warm water, you never know, but with zero model support and little convection, I don't think anything comes of this system.

Your last sentence is exactly how I view it right now. It is purely a continued convection flare-up that will keep me looking (don't care about the models cause they never sense these kind of developments). If all convection dies off I'll be done with it.

[ozonepete]

You never know OP! If something does ever become of this, you got 1st dibs on it!

Yeah, that's true, but I'm just following it out of "tropical boredom", lol.

[ozonepete]

It has drifted southeastward but is still there. Just keepin' an eye on it while all else is pretty quiet.

[gatorcane]

Yep it is still there with a little bit more convection. Bear watch officially in effect!

[Annie Oakley]

if move were will it go?

Can't tell because it would have to develop first (and reach a certain level in the atmosphere) before we could use forecast steering currents to see where it would go. But for the next few days at least the steering winds will remain dead there so it's not going anywhere.

ok ty ( i notice that area too put their almost dont form if upper low)

floridasun you are one of my favorite posters. Just wanted to say that.....

[ozonepete]

Yep it is still there with a little bit more convection. Bear watch officially in effect!

Persistence of convection is what keeps us interested.

[ozonepete]

Convection really blew up over it today and it developed lower convergence and upper divergence with vorticity down to 850mb. The convection has just died off this evening but it still has spin.

[Annie Oakley]

So what is spin without convection-false something? Or a dying storm?

[ozonepete]

To keep it simple let's just talk about a moist environment such as this one. Spin (or vorticity) can only cause convection if there is some vertical motion as well. In other words, if you picture our spinning disturbance here as a spinning donut a few thousand feet above the ocean, that spin isn't enough by itself to get the air to rise from underneath it and thus cause thunderstorms to blossom (rapidly rising warm moist air currents). There needs to be an influence from underneath our spinning air to cause air to rush in towards the bottom of the disturbance, or an influence from above to cause air to rush away from the top. Either (or both together) will cause the air to start moving up into the spinning air columns and this rising spinning air will cause thunderstorms (convection) to develop. The fact that this disturbance had such good convection today but lost it all at sunset is probably due to the rising air currents provided by heating of the surface layer from daytime solar input. If that's the case, it should flare up some good convection again tomorrow. But I'm not sure this small system has much oomph left in it. Just interesting to watch it and learn some physics from it.

[Annie Oakley]

What a post. Thank you so much for sharing your knowledge. Please keep inspiring us all.
You always treat us here as equals here lol and that is a gift. You also have an amazing gift for patience.
Appreciate you

[ozonepete]

[ozonepete]

Still spinning around. After drifting southeastward over the last few days it started drifting back toward where it came from and is actually right about back where it started. Now clearly moving northwestward, albeit very slowly. I suspect convection will really pop over this today since there should be good upper level divergence over it. The clue is that convection is already starting to fire before sun-up adds its insolar heating effect.