At the time I'm writing this, Tropical Depression Pali is rapidly
weakening as it grinds its tropical gears within 2.5 degrees latitude of
the equator. Two days ago, I was thinking that Pali had at least a
fighting chance to retain its rotational integrity and cross the
equator, despite the lack of a meaningful Coriolis force at these very
low latitudes. In other words, I was banking on inertia and angular
momentum to offset the dwindling contribution of the Coriolis force to
Pali's rotation.
Alas, the very small contribution of the Coriolis force to the tropical cyclone's rotation made the storm increasingly vulnerable to the deleterious effects of vertical wind shear. Below is the deep-layer shear (850-mb to 200 mb), valid at 15 UTC this morning. Southwesterly wind shear, with magnitudes on the order of 20 to 25 knots over Pali, have been dramatically disruptive in this low-latitude environment.
Tropical Depression Pali, marked by an "L," is rapidly weakening in an environment characterized by moderate southwesterly vertical wind shear of 20-25 knots. The magnitudes of the vertical-shear vector (yellow contours) are plotted in knots. The directions of the vertical-shear vector are represented by streamlines. Courtesy of CIMSS.
In summary...inertia and angular momentum could have given Pali at least a chance at an equatorial crossing, but moderate vertical wind shear at these very low latitudes has been a bully, taking full advantage of Pali's vulnerability in this tiny-Coriolis environment.
In my view, Pali made an admirable run at the equator. A truly fascinating storm!
Best,
Lee
Alas, the very small contribution of the Coriolis force to the tropical cyclone's rotation made the storm increasingly vulnerable to the deleterious effects of vertical wind shear. Below is the deep-layer shear (850-mb to 200 mb), valid at 15 UTC this morning. Southwesterly wind shear, with magnitudes on the order of 20 to 25 knots over Pali, have been dramatically disruptive in this low-latitude environment.
Tropical Depression Pali, marked by an "L," is rapidly weakening in an environment characterized by moderate southwesterly vertical wind shear of 20-25 knots. The magnitudes of the vertical-shear vector (yellow contours) are plotted in knots. The directions of the vertical-shear vector are represented by streamlines. Courtesy of CIMSS.
In summary...inertia and angular momentum could have given Pali at least a chance at an equatorial crossing, but moderate vertical wind shear at these very low latitudes has been a bully, taking full advantage of Pali's vulnerability in this tiny-Coriolis environment.
In my view, Pali made an admirable run at the equator. A truly fascinating storm!
Best,
Lee
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