1. Shower activity has increased during the past 24 hours in
association with a nearly stationary area of low pressure located a
few hundred miles south-southwest of Acapulco, Mexico.
Environmental conditions are expected to become more conducive for
development, and a tropical depression could form this weekend or
early next week while the low begins moving west-northwestward to
northwestward, parallel to the coast of Mexico.
*Formation chance through 48 hours...low...20 percent
*Formation chance through 5 days...high...70 percent
TROPICAL DEPRESSION SEVENTEEN-E DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL EP172016
900 PM MDT SAT SEP 17 2016
The broad area of low pressure that NHC has been monitoring for
several days south of Mexico has finally acquired enough
organization to be classified as a tropical depression with an
initial intensity of 30 kt. Microwave data during the day showed
several swirls rotating around the larger circulation, but during
the past couple of hours, satellite images show that a well defined
center became embedded within the convection, and it is the one NHC
is currently tracking.
The shear is forecast to be light for the next day or so, allowing
the depression to intensify some. After 48 hours, both an increase
of shear and an encounter with cooler waters should result in
weakening as indicated in the NHC forecast.
The best estimate of the initial motion is toward the northwest
or 305 degrees at 14 kt. The depression is being steered by a
strong subtropical high over northern Mexico. In about 36 hours,
the depression will reach the southwestern edge of the high, and
will likely turn northward with a decrease in forward speed. The
NHC forecast follows very closely the multi-model consensus TVCN.
This track keeps the cyclone well removed from the southwest coast
of Mexico.
TROPICAL STORM PAINE DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL EP172016
300 AM MDT SUN SEP 18 2016
The system's cloud pattern has very quickly exhibited increased
organization. A relatively long band with very cold-topped
convection wraps in toward the low-level center. The low-level
center appears to be located near the eastern end of this band,
suggesting that some northeasterly shear persists. A Dvorak
classification of T2.5 from SAB and the latest UW-CIMSS ADT value of
2.8 are used to raise the initial intensity estimate to 35 kt.
The center location and hence the initial motion are more uncertain
than normal, especially with no recent microwave passes and after a
center reformation yesterday. The best estimate is 310/12. Paine
should be steered generally northwestward around the southwestern
periphery of a mid-level high over the Rio Grande Valley during the
next 24 to 36 hours. After that time, the cyclone is expected to
then turn north-northwestward and northward when it encounters a
break in the ridge caused by a cut-off low retrograding offshore the
California coast. The new track forecast is shifted a bit to the
right of the previous one after 12 hours, following the multi-
model consensus.
The shear affecting the cyclone is forecast to reach a relative
minimum today while Paine is still moving over warm waters. This
should allow the cyclone to intensify at near a climatological rate
of one T-number per day during the next 24 to 36 hours.
Southwesterly shear should abruptly increase by late Monday in
association with the cut-off low around the time Paine crosses the
26-deg isotherm. This should bring whatever intensification is
occurring to a halt. Global models show Paine decoupling as the
shear reaches 25-30 kt in 2 to 3 days, while the storm is moving
over 22-24 deg C waters. Paine is thus shown degenerating into a
remnant low in 72 hours, and dissipating before 96 hours. The NHC
is higher than the previous one out to 36 hours and is about the
same after that, close to the multi-model consensus.
Deep-layer moisture associated with Paine is expected to be
advected into extreme southern California and the Desert Southwest
in a couple of days, which could enhance the potential for unusual
September rains across this region.
HURRICANE PAINE DISCUSSION NUMBER 9
NWS NATIONAL HURRICANE CENTER MIAMI FL EP172016
800 PM PDT MON SEP 19 2016
Paine is quickly losing organization this evening. A very timely
2334 UTC SSMIS microwave overpass shows that the low- and mid-level
centers are beginning to decouple due to increasingly south-
southwesterly shear. As a result, subjective Dvorak data T-numbers
have started to decrease, and the initial wind speed has been
reduced to 70 kt for this advisory. Paine will be moving over much
cooler SSTs and into a higher shear environment during the next day
or so. This should cause rapid weakening, and Paine is expected to
become a tropical storm by early Tuesday, and degenerate into a
remnant low within 36 hours.
Paine appears to be slowing down, with an initial motion estimate
of 345/11 kt. The track forecast philosophy remains unchanged from
before, with the tropical cyclone moving northward, then north-
northeastward between a deep-layer ridge to its northeast
and an upper-level low to its northwest. As Paine weakens and
becomes a shallow system, it should decelerate when it comes
under the influence of weaker low-level flow west of the Baja
California peninsula. The track models are in good agreement,
and the NHC foreast is near the middle of the guidance envelope.
Deep-layer moisture associated with Paine or its remnants is
expected to spread over portions of the northern Baja California
peninsula of Mexico and the southwestern United States during the
next day or two. This could enhance the rainfall potential in these
areas.
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