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Tropical Storm MADELINE Forecast Discussion (Text)


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000
WTPZ44 KNHC 272033
TCDEP4

TROPICAL STORM MADELINE DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP142016
200 PM PDT SAT AUG 27 2016

GOES-West visible imagery shows that the center of Madeline is
located on the northeastern edge of a ragged area of central
convection, with a large convective band wrapping around the western
semicircle of the circulation.  The initial intensity estimate is 50
kt, which is a blend of the latest subjective and objective Dvorak
classifications.  The SHIPS model output shows the vertical shear
decreasing below 10 kt by tonight, while Madeline is moving over
SSTs above 27C.  This environment should allow for some additional
strengthening during the next 24 to 36 hours.  After that time, the
tropical cyclone will be moving over cooler SSTs and into a drier
environment, with mid-level relative humidity values falling below
50 percent.  This should result in gradual weakening, followed by
steadier weakening later in the period as the vertical wind shear
increases above 20 kt.  The new NHC intensity forecast is a little
higher than the previous one in the short range given the observed
strengthening, and is similar afterward.  This forecast is close to
or a bit below the latest IVCN consensus.

The initial motion estimate is 305/09.  The track forecast reasoning
remains unchanged, as Madeline should continue moving generally
northwestward for the next 48 hours under the influence of mid-level
ridge centered well to its northeast.  Later in the period, a
strengthening mid-level ridge north of the Hawaiian Island will
become the dominant steering mechanism and result in a westward or
slightly south of due westward track.  Through 72 hours the new NHC
forecast is largely and update of the previous near one and close to
the TVCN consensus near the middle of the guidance envelope.  At
days 4 and 5 the global models have shown run-to-run inconsistency
about the details of Madeline's track near the Hawaiian Islands.
The latest runs of the ECMWF, GFS, and HWRF have shifted south, with
a track south of the Big Island, while much of the rest of the
guidance is farther north.  The NHC track has been shifted southward
a little at days 4 and 5, but lies a little north of the multi-model
consensus and well north of the southerly set of models.

Given the lack of consistency in the track guidance, the confidence
in the track foreast late in the period is lower than usual and it
is too early to determine what impacts Madeline could have on the
Hawaiian Islands late in the forecast period.  It is important to
remind users that the average day 4 and 5 track forecast errors for
eastern Pacific tropical cyclones are around 145 and 170 miles,
respectively.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 15.7N 139.3W   50 KT  60 MPH
 12H  28/0600Z 16.4N 140.3W   60 KT  70 MPH
 24H  28/1800Z 17.3N 141.5W   65 KT  75 MPH
 36H  29/0600Z 18.3N 143.0W   70 KT  80 MPH
 48H  29/1800Z 19.3N 144.5W   70 KT  80 MPH
 72H  30/1800Z 20.4N 148.2W   65 KT  75 MPH
 96H  31/1800Z 20.5N 152.5W   60 KT  70 MPH
120H  01/1800Z 20.0N 157.0W   50 KT  60 MPH

$$
Forecaster Brennan



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Page last modified: Saturday, 27-Aug-2016 20:34:06 UTC