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Tropical Storm Greg Discussion Number  26
NWS National Hurricane Center Miami FL       EP072017
200 PM PDT Sun Jul 23 2017

Greg has had a large burst of deep convection during the past
several hours, although cloud tops have begun to warm just
recently.  A 1748 UTC ASCAT-B pass showed maximum winds of 40 kt,
but subjective and objective Dvorak estimates have all increased to
T3.0/45 kt.  Therefore, the initial intensity will remain 45 kt,
with the assumption that the resolution of the scatterometer missed
higher winds.

Greg is moving westward, or 270/12 kt, to the southeast of a low-
to mid-level anticyclone centered northeast of Hawaii.  Although
the ridging is not expected to weaken, it is forecast to expand and
shift westward, which could allow Greg to turn west-northwestward
in about 36 hours.  A turn back toward the west is expected by day 4
when it becomes a remnant low and is steered by the low-level trade
winds.  The track models have moved northward on this cycle,
leaving the previous official forecast along the southern edge of
the guidance envelope.  This necessitated that the new NHC forecast
be nudged northward as well, but it is still south of the TVCN
multi-model consensus for at least the first 48 hours.

The thermodynamic environment appears to be the limiting factor on
Greg's intensity, since the vertical shear is expected to remain
low for the next 48 hours.  Visible satellite imagery shows a large,
stable stratocumulus field out ahead of the cyclone, and
lower-level water vapor imagery from GOES-16 shows a lot of
mid-level dry air.  Therefore, Greg is likely to only maintain its
intensity for the next 24 hours and then gradually weaken due to
the dry air, increasing shear, and cooler sea surface temperatures.
No significant changes were required to the NHC intensity forecast,
and Greg is still expected to degenerate into a remnant low on day
4.

FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 14.4N 130.1W   45 KT  50 MPH
 12H  24/0600Z 14.5N 131.8W   45 KT  50 MPH
 24H  24/1800Z 14.8N 133.8W   45 KT  50 MPH
 36H  25/0600Z 15.2N 135.4W   40 KT  45 MPH
 48H  25/1800Z 15.9N 136.8W   40 KT  45 MPH
 72H  26/1800Z 17.1N 139.6W   30 KT  35 MPH
 96H  27/1800Z 17.1N 142.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  28/1800Z 16.3N 145.6W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

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