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TROPICAL STORM COLIN DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL032016
400 AM CDT MON JUN 06 2016

Colin remains poorly organized this morning.  Surface observations
and data from NOAA and Air Force Reserve Hurricane Hunter aircraft
suggest that at least two small-scale circulation centers are
present, one near an intense burst of convection around 24.5N 85.5W
and the other well to the west-northwest near 25.5N 89W.  The low
confidence initial position splits the difference between these two
features.  The Air Force aircraft reported 850-mb flight-level
winds of 71 kt and estimated 60 kt surface winds on the SFMR
instrument.  However, these winds were measured in the
aforementioned convection, and it is unclear how representative they
are.  There is sufficient data to justify increasing the initial
intensity to 45 kt.

The cyclone appears to be moving faster, with the initial motion
now 015/12.  The track forecast reasoning again has not changed from
the previous advisory.  Over the next day or so, Colin should move
north-northeastward to northeastward in the flow between a
deep-layer trough over the western and northern Gulf of Mexico and a
ridge over the subtropical western Atlantic.  After that time, the
cyclone will become embedded in strong southwesterly flow associated
with a large baroclinic low over the eastern United States.  The
track guidance has nudged northward since the previous advisory, and
the new forecast track, which lies near the consensus models, is
also nudged northward.

The poor organization and the presence of moderate vertical wind
shear suggest that significant strengthening is unlikely before
Colin makes landfall in Florida in less than 24 hours.  The global
models forecast winds of near 50 kt as Colin moves over the Atlantic
and begins extratropical transition, and the latter part of the
intensity forecast is based on this guidance.  The model guidance
forecasts that extratropical transition should be complete by about
72 hours.

It is important to emphasize that one should not focus on the exact
forecast track of this system.  Strong winds, heavy rains and
coastal flooding are likely to occur well to the east of the center.


FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 25.2N  87.4W   45 KT  50 MPH
 12H  06/1800Z 27.6N  85.8W   45 KT  50 MPH
 24H  07/0600Z 30.7N  81.9W   45 KT  50 MPH...INLAND
 36H  07/1800Z 33.8N  76.2W   50 KT  60 MPH...OVER WATER
 48H  08/0600Z 37.6N  67.8W   50 KT  60 MPH
 72H  09/0600Z 45.0N  50.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  10/0600Z 50.0N  36.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  11/0600Z 54.0N  29.9W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven

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