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Tropical Storm Erick Discussion Number   5
NWS National Hurricane Center Miami FL       EP062019
500 AM HST Sun Jul 28 2019

The convective cloud pattern has changed little overall since the
previous advisory, with the main cloud mass displaced into the
southern semicircle due to some northerly mid-level shear. A
late-arriving 0615Z ASCAT-C scatterometer pass along with passive
microwave imagery indicate that the low-level center is positioned
near the northern edge of the central convective cloud mass.
However, the upper-level outflow has continued to improve and expand
in all quadrants. The scatterometer pass showed only a few 33-kt
surface wind vectors in the northeastern quadrant, so the advisory
intensity remains at 35 kt, which is in agreement with 35-kt Dvorak
satellite estimates from both TAFB and SAB.

The initial motion is 275/15 kt. A slight westward jog has occurred
during the past 6 hours, likely due to the southward shift in the
convective cloud mass. However, resumption of the earlier base
motion of 280 degrees is expected later today when the shear
decreases and the convective cloud pattern becomes more symmetrical.
Overall, there is no significant change to the previous forecast
track rationale. A narrow but well-defined low to mid-level ridge is
forecast by the global models to build westward across the Hawaiian
Islands through the entire forecast period, which is expected to
keep Erick moving generally westward to slightly west-northwestward.
On the forecast track, Erick is expected to cross into the Central
Pacific basin on Tuesday, and the new NHC model guidance remains in
good agreement on this track scenario. The new official forecast
track is a little south of the previous advisory track, mainly due
to the more southerly initial position, and lies close to a blend of
the consensus track models HCCA and TVCE.

Convective banding has started to increase during the past few
hours, along with the development of a small CDO feature. The
aforementioned ASCAT-C pass revealed that Erick has a small radius
of maximum winds (RMW) of about 20 nmi. The small RMW, low vertical
wind shear of about 5 kt, and SSTs near 28C support at least steady
strengthening at a typical climatological rate of 20 kt per 24 hours
for the next 2-3 days. As a result, Erick is forecast to become a
hurricane in 36 hours. Although rapid intensification (RI) is a
possibility due to the small RMW and low shear, a dry mid-level
environment is expected to hinder RI through 72 hours when stronger
vertical wind shear is forecast to affect the cyclone and disrupt
the intensification process. Thereafter, steady weakening
due to westerly wind shear increasing to more than 20 kt is
expected, resulting in Erick becoming a tropical storm by 120 hours.
It is worth mentioning that although the Navy COAMPS model is
forecasting Erick to become a category-4 hurricane by 72 hours, this
scenario has been disregarded at this time due to the abundance of
dry mid-level surrounding cyclone. The official intensity forecast
is similar to the previous NHC advisory, and closely follows the
HCCA corrected consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  28/1500Z 12.3N 129.8W   35 KT  40 MPH
 12H  29/0000Z 12.6N 132.0W   45 KT  50 MPH
 24H  29/1200Z 13.1N 134.9W   55 KT  65 MPH
 36H  30/0000Z 13.6N 137.6W   65 KT  75 MPH
 48H  30/1200Z 14.3N 140.3W   75 KT  85 MPH
 72H  31/1200Z 15.6N 145.0W   85 KT 100 MPH
 96H  01/1200Z 16.6N 149.6W   65 KT  75 MPH
120H  02/1200Z 17.1N 154.8W   45 KT  50 MPH

$$
Forecaster Stewart

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