Question

[Tip]

How can the convection remain stationary through the day when there is obviously a strong easterly flow?

[Steve H.]

That easterly flow is at the low levels. The shear is at the upper levels of the atmosphere. Cheers!!

[Tip]

Ok, but why doesn't the wave move east in the genral low level flow like most waves?

[ColdFront77]

Most tropical waves do not move eastward in the latitude 90L is located. The steering is toward the west, so 90L is moving mainly toward the west.

[Tip]

Sorry I got a little dyslexia lol. I meant to say the wave should be traveling west in the easterly flow. However, the point is that it doesn't seem to have moved hardly at all today.

[wxman57]

The answer here is really quite simple. With a weak system (tropical wave, weak disturbance, disorganized tropical depression/storm), the tendency is to focus on the movement of the convection rather than the low-level feature itself. This can get you into trouble when you estimate the general movement, particularly at night, when the tendency is to for your eye to follow the bright colors aloft rather than the dull gray clouds near the surface. I would suggest that you run a visible satellite loop and <b>ignore</b> the convection. Watch the wave itself - the lower-level stratocumulus axis. What you will see is that the wave axis has been tracking steadily westward all day long. But look where the convection is firing along the wave. Early this morning, the onvection was firing along the <b>leading</b> edge of the wave, being enhanced by the upper-level low to the north. But as the wave continued moving westward during the day, the convection fired along the crest of the wave and then (now) along the eastern (trailing) edge of the wave. So the convection has been firing in the same spot all day as the wave moved on past. You can actually follow the remnants of that tiny eddy from near 57W to almost 61W through the day today - that's why tstms are beginning to fire across the northern Windward Islands now.

This would suggest that the convection should be diminishing tonight as the wave moves past that area of enhanced lift produced by the upper low.

[ColdFront77]

Good point, wxman. The convection and the center of weaker systems makes it difficult to tell at first glance the direction of movement.

[Tip]

Thanx for the explanation Wxman57.