Tropical Depression Eight Discussion Number 1
NWS National Hurricane Center Miami FL AL082019
500 PM AST Tue Sep 03 2019
Satellite images indicate that the broad area of low pressure over
the eastern Atlantic has become better defined during day, with
rainbands forming on the eastern side of the circulation. This
structure is good enough for a tropical depression, and the initial
wind speed is set to 30 kt, which agrees with earlier ASCAT passes
that showed 25-30 kt.
The initial motion estimate is 310/7 kt. A general northwestward
motion is anticipated during the next several days, faster by the
weekend, as the system is steered by a strengthening eastern
Atlantic ridge. One source of uncertainty in the future track is
how much the cyclone is affected by a developing mid-level low
around 25N45W in a few days. This feature could briefly induce a
north-northwestward motion on Friday, and later west-northwestward
on day 5 depending on exactly how close the new tropical cyclone
gets to the mid-level low. For now it is best not to bite off on
any particular model solution, since the intensity and depth of the
cyclone isn't certain at this range. Thus, the forecast is close
to the Atlantic model consensus TVCA, shaded a bit on the fast side
assuming the system keeps some vertical depth.
Although the depression is forecast to be in a low-shear environment
during the next couple of days, marginal water temperatures should
keep the strengthening rate modest. The intensity forecast is
complicated beyond that point due to the system's interaction with
the mid-level low, drier air in the mid-levels, and increasing
waters temperatures. This mixed bag of factors makes the forecast
rather murky, with any intensity changes at longer range having low
predictability at this point. Therefore, the forecast is leveled
off at long range, similar to the NOAA corrected-consensus model
HCCA, but this uncertain forecast could require a great deal of
revision later tonight or tomorrow.
1. Recent satellite-derived surface winds indicate that the low
pressure area located a few hundred miles west of the Cabo Verde
Islands is becoming better defined. Associated thunderstorm
activity has been increasing and showing signs of organization, and
a tropical depression is expected to form later today while the
system moves generally northwestward across the eastern tropical
Atlantic Ocean.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 5 days...high...90 percent.
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