Hurricane Aletta Discussion Number 9
NWS National Hurricane Center Miami FL EP022018
900 PM MDT Thu Jun 07 2018
Based on how Aletta looked last evening, it would have been hard to
imagine the cyclone improving in structure so drastically. Yet, the
hurricane has continued to improve in organization and has deep
convection with cloud tops as cold as -85C completely surrounding a
ragged, cloud-filled eye. Dvorak classifications have increased to
T5.0/90 kt from TAFB and SAB, while objective guidance from the
UW-CIMSS ADT and SATCON have increased more modestly to between
75-80 kt. Based on these data, Aletta's current intensity is
estimated to be 85 kt. Since Aletta's estimated intensity 24 hours
ago was 45 kt, the cyclone's recent strengthening meets the
criterion for rapid intensification.
Aletta appears to have another 24 hours or so before vertical shear
gradually increases, and 48 hours before sea surface temperatures
become marginal to support further strengthening. Therefore,
additional intensification is anticipated during the next 24 hours,
and the new NHC official forecast brings Aletta's intensity to just
below major hurricane status. The chance of a another 20-kt
increase in the next 12 hours is just under 50 percent, so it's not
out of the question that Aletta could reach major hurricane
strength on Friday. Weakening is anticipated to begin by 36 hours,
and the weakening rate should be rather fast in 3 to 4 days due to
stronger shear and colder waters. The updated NHC forecast is
close to HCCA and the intensity consensus for the first couple of
days but then is above most of the guidance after 48 hours to
maintain continuity with the previous forecast. The GFS and ECMWF
models show Aletta's convection dissipating in about 4 days, so the
NHC forecast now calls for the cyclone to become a remnant low by
day 5.
Aletta is being steered slowly west-northwestward, or 300/5 kt,
around a mid-level ridge located over northwestern Mexico and
toward a break in the ridge located west of the Baja California
peninsula. Because the hurricane has strengthened more than
previously expected, it has taken a jog toward the north, closer to
where more aggressive models such as the GFS and HWRF had been
predicting. With the additional strengthening anticipated, the NHC
track forecast largely discounts the ECMWF solution, which is an
outlier to the south of the other models, and lies farther north
close to the TVCE model consensus and HCCA models.
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