ATL: INVEST 93L - Discussion

[AlphaToOmega]

Tons of models develop Invest 93L, and only a few models develop Invest 92L. However, the global models are more enthusiastic about the wave west of Invest 93L. Invest 93L still seems to be in the best spot for tropical development. Upper ocean heat content is only marginal where Invest 93L is currently located; but the the atmospheric pattern for Invest 93L seems to be pretty favorable, for wind shear is only 10 knots where Invest 93L is located. This wave is surrounded by a tropical wave to its west and a tropical wave to its east, so dry air is not going to be a factor. If Invest 93L could make it past 50° W, it would develop much more easily.

[aspen]

HWRF ends with pretty strong Hurricane.

HWRF does poorly with invests especially in this area. I remember it constantly blew up pre-Gonzalo / early stages of TD 7 up to a potent hurricane (one of the reasons why the intensity forecast was so high IIRC) and it ended up peaking at 60-70 mph. HMON doesn’t even develop it so I’d toss this run out until we get a clearer picture or more agreement from other models

Aren’t the trade winds weaker now? That was why it busted so badly with Elsa, although it did correctly forecast a compact Cat 1 passing through the Lesser Antilles.

[AlphaToOmega]

Which global model best handles monsoon troughs?

[cycloneye]

Showers and thunderstorms associated with an area of low pressure
located over the tropical Atlantic about midway between the Cabo
Verde Islands and the Lesser Antilles have become more concentrated
since yesterday. Environmental conditions are expected to become a
little more favorable for gradual development, and this system
could become a tropical depression within the next few days. The
system is forecast to move slowly toward the west-southwest or west
during the next couple of days, and then move a little faster toward
the west by mid-week.
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 5 days...medium...40 percent.

[tolakram]

Which global model best handles monsoon troughs?

None?

I know we all expect the wave ahead of 93 to be tagged, but there's no hard and fast rule as far as I know, so whatever develops, if anything, might be 93.

[wx98]

Tons of models develop Invest 93L, and only a few models develop Invest 92L. However, the global models are more enthusiastic about the wave west of Invest 93L. Invest 93L still seems to be in the best spot for tropical development. Upper ocean heat content is only marginal where Invest 93L is currently located; but the the atmospheric pattern for Invest 93L seems to be pretty favorable, for wind shear is only 10 knots where Invest 93L is located. This wave is surrounded by a tropical wave to its west and a tropical wave to its east, so dry air is not going to be a factor. If Invest 93L could make it past 50° W, it would develop much more easily.

There is almost always dry air. It appears quickly and swiftly like those phantom ULLs that love to shear storms apart.

[Category5Kaiju]

Something I have learned from continuously tracking these systems since 2017: in many cases when the dry air looks to be an inhibiting factor, some of these waves actually perform better than expected and blow up in convection and shield themselves from the dry air with a moisture bubble. So, just something to watch, all I am saying is unless I see it actually happen real time and that there is substantial evidence to prove such, I assume that the dry air won’t be an automatic death knell to these waves, particularly 93L.

[NXStumpy_Robothing]

In most scenarios, dry air on the periphery of a system will not be enough on its own to be an inhibiting factor on the eventual strength of a cyclone (though it does usually mean a system will be smaller than otherwise anticipated). When a tropical cyclone is surrounded by dirty air, it can and will often form a insulated moisture pouch thanks to the thermodynamics that power recurring convection in such a system. Instead, what you need is to have some amount of shear that will impact the core circulation. Obviously, the weaker the cyclone, the closer to the ground this shear needs to be in order to allow dry air to infiltrate the system.

In 93L's case - it's currently flirting the boundary between lighter overall shear and upper-level divergence aloft, and greater low-level shear/lower-level divergence, and it's displayed quite easily with its convective pattern, which is pulsing down from its overnight peak. It remains to be seen if it can regenerate that previously-impressive convection it had overnight, or if that lower-level easterly shear will continue to allow dry air to infiltrate the small low pressure area at the center. As with most things in the tropics, we just have to wait and see what it does.

[aspen]

The vorticity signature for this looks quite good — stronger than 94L and whatever’s left of 92L — but convection has significantly waned as a result of dry air and Dmin. 93L needs to pop some more fast before it’s killed off, although if it does die, then there would probably be less vorticity competition with 94L.

[Sciencerocks]

[cycloneye]

Showers and thunderstorms associated with an area of low pressure
located over the tropical Atlantic about midway between the Cabo
Verde Islands and the Lesser Antilles have diminished this morning.
Although environmental conditions appear to be only marginally
conducive for development, this system could still become a
tropical depression later this week while it moves toward the
west-southwest or west at around 10 mph.
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 5 days...medium...40 percent.

[Sciencerocks]

[cycloneye]

Disorganized showers and thunderstorms have changed little in
association with an elongated low pressure system located over the
tropical Atlantic about midway between the Cabo Verde Islands and
the Lesser Antilles. Although environmental conditions appear to be
only marginally conducive for development, this system could still
become a tropical depression later this week while it moves toward
the west or west-southwest at around 10 mph.
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 5 days...medium...40 percent.

[Sciencerocks]

[ElectricStorm]

Looks like I may have been wrong about this one developing. All the attention is on 94L now

2. Disorganized showers and thunderstorms have changed little in
association with an elongated low pressure area located about 1000
miles east of the Lesser Antilles. Development of this system is
becoming less likely during the next few days while it moves toward
the west or west-southwest at around 10 mph.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...low...30 percent.

[AlphaToOmega]

Still to early to say requiescat in pace

2. Disorganized showers and thunderstorms have changed little in
association with an elongated low pressure area located several
hundred miles east of the Lesser Antilles. Development of this
system is becoming less likely during the next few days while it
moves toward the west or west-southwest at around 10 mph.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...low...20 percent.

[Category5Kaiju]

RIP 93L, at least you did your role by moistening the air for the next waves to come