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TROPICAL STORM OTTO DISCUSSION NUMBER  18...CORRECTED
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP222016
300 AM CST FRI NOV 25 2016

Corrected for Central Standard Time instead of Central Daylight
Time in product header.

The cloud pattern of Otto is rather ragged this morning after the
circulation moved offshore of Central America. Shortwave infrared
imagery suggests that there may now be some tilt to the circulation,
with the low-level center possibly located south of the mid-level
center. However, this is quite uncertain given the lack of microwave
imagery overnight. Based on this apparent decrease in organization,
the initial intensity is set to 50 kt, a little below the latest
Dvorak estimates of T3.5/55 kt from TAFB and SAB.

The intensity forecast is problematic. Most of the guidance suggests
that Otto will maintain its current intensity for the next 48 hours
or so while the cyclone moves over SSTs of 28-29C but with
continued southeasterly shear of 15-20 kt. Through this time the
NHC intensity forecast is near or a bit below the IVCN intensity
consensus. By day 3, the shear begins to decrease, but the
atmosphere dries out as Otto interacts with outflow from a Gulf of
Tehuantepec gap wind event. The global models show Otto weakening
late in the period, and that trend is reflected in the official
forecast, which continues to show Otto becoming a remnant low at day
5. However, given the uncertainty in the current structure of Otto
and the interplay between several competing environmental factors
during the forecast period, confidence in the intensity forecast is
lower than usual.

The initial motion estimate is a somewhat uncertain 265/12. I
shifted the initial position a little to the south to account for
the possible tilt in the circulation mentioned above. This resulted
in a southward shift of the track guidance envelope and the NHC
forecast even though the synoptic reasoning has not changed. An
amplifying mid-level ridge will steer Otto south of due west at
around 15 kt for the next 48 hours. Then, as the ridge weakens late
in the period, a slowing forward speed and gradual poleward turn are
expected. The new NHC track is close to the latest multi-model
consensus, but lies north of the latest GFS and ECMWF predictions.

FORECAST POSITIONS AND MAX WINDS

INIT  25/0900Z 10.5N  86.9W   50 KT  60 MPH
 12H  25/1800Z 10.1N  88.8W   50 KT  60 MPH
 24H  26/0600Z  9.5N  91.6W   50 KT  60 MPH
 36H  26/1800Z  9.2N  94.6W   50 KT  60 MPH
 48H  27/0600Z  9.0N  97.5W   45 KT  50 MPH
 72H  28/0600Z  9.3N 103.0W   40 KT  45 MPH
 96H  29/0600Z 10.5N 106.0W   35 KT  40 MPH
120H  30/0600Z 12.5N 107.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brennan

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