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Tropical Storm Adrian Discussion Number   2
NWS National Hurricane Center Miami FL       EP012017
1000 PM CDT Tue May 09 2017

Although outer banding features have weakened somewhat since the
previous advisory, the inner-core convective pattern has improved,
including the possible development of a small, mid-level eye feature
as noted in 0059Z SSMI/S microwave data. The upper-level outflow is
improving and expanding in all quadrants, except to the east where
is being restricted by upper-level easterly flow. Satellite
classifications are a consensus T2.5/35 kt from TAFB and SAB, so the
depression has been upgraded to tropical storm status. This makes
Adrian the earliest tropical storm to form in the eastern North
Pacific basin during the satellite era.

The initial motion estimate is 290/06 kt. Adrian is moving slowly
west-northwestward along the southern periphery of a deep-layer
ridge located over the central and southwestern Gulf of Mexico. The
global and regional models are fair agreement on this ridge pattern
remaining basically static for the next 48-72 hours, so little
change in the west-northwestward motion of the tropical storm is
expected during that time. By 72 hours and beyond, the ridge to the
north of Adrian is forecast to gradually weaken and eventually break
down by 120 hours as the large-scale, high-amplitude flow pattern
across the United States weakens and shifts eastward. This pattern
change is expected to result in weak southwesterly steering flow
developing, causing the cyclone to slow down significantly and turn
northeastward. The 12Z ECMWF model run does not develop the cyclone
beyond its current intensity, which results in a very shallow system
being steered northeastward by increasing southwesterly low-level
monsoon flow by 72 hours and beyond. This scenario seems unlikely at
this time given that Adrian is forecast to strengthen into a
hurricane and become more vertically deep, so less weight has been
placed on the weaker ECMWF solution. The official forecast track is
similar to the previous advisory track, and lies close to a blend of
the various consensus models.

Earlier scatterometer wind data and recent microwave satellite
imagery indicate that Adrian has developed a small radius of maximum
winds of 25-30 nmi. This tight inner-core wind field, along with
SSTs exceeding 30 deg C, a moist mid-level environment, and only
modest wind shear of 10-15 kt support steady intensification
throughout the forecast period. By 96-120 hours, increasing
southerly to southwesterly vertical wind shear could disrupt the
intensification process, but Adrian is expected to already be a
hurricane by that time. The official intensity forecast follows the
strengthening trend of the previous advisory, but is a little
stronger and is similar to the SHIPS model forecast due to the
non-development of Adrian noted in the HWRF and Navy COAMPS models,
which is causing a low bias in the IVCN/ICON consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  10/0300Z  9.5N  92.3W   35 KT  40 MPH
 12H  10/1200Z  9.8N  93.1W   40 KT  45 MPH
 24H  11/0000Z 10.3N  94.1W   50 KT  60 MPH
 36H  11/1200Z 10.8N  95.2W   55 KT  65 MPH
 48H  12/0000Z 11.2N  96.2W   60 KT  70 MPH
 72H  13/0000Z 12.1N  97.1W   70 KT  80 MPH
 96H  14/0000Z 13.1N  96.8W   80 KT  90 MPH
120H  15/0000Z 14.1N  96.0W   85 KT 100 MPH

$$
Forecaster Stewart

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