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Tropical Storm Karina Discussion Number   2
NWS National Hurricane Center Miami FL       EP162020
300 AM MDT Sun Sep 13 2020

Recent scatterometer data showed an area of 30-35 kt winds within 
about 80 n mi of the center of Tropical Depression Sixteen-E in the 
southwestern quadrant.  Based on this data, along with 35-40 kt 
intensity estimates from TAFB and the CIMSS satellite consensus, 
the depression is upgraded to Tropical Storm Karina with an initial 
intensity of 35 kt.  Satellite imagery show that the system is 
still being affected by northeasterly vertical shear, with the 
low-level center exposed to the northeast of the main convective 
mass.

The initial motion is now 310/10.  The global models forecast a 
mid-level ridge to build westward to the north of Karina in a day or 
two, causing the cyclone to move west- northwestward.  A more 
westward motion is expected near the end of the forecast period as a 
weakening Karin is steered more by the low-level trade winds.  The 
track guidance is in fair agreement with this scenario, although 
there is some spread in the forward speed, possibly due differences 
in how Karina interacts with the larger ITCZ/monsoon trough 
circulation, including the remnants of Invest 91E.  The new forecast 
track will follow the forward speed of the consensus models and has 
only minor adjustments from the previous track.

The forecast track takes the center of Karin over cooler water, 
with the system crossing the 25-26C isotherms in 48-72 h.  Present 
indications are that the shear will decrease a little before the 72 
h point, so the intensity forecast calls for gradual strengthening 
during that time.  After 72 h, the cooler water and dry air 
entrainment should cause weakening.  The new intensity forecast has 
some minor adjustments from the previous forecast, and it is in 
best agreement with the HCCA corrected consensus model and the 
Florida State Superensemble.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0900Z 17.4N 113.8W   35 KT  40 MPH
 12H  13/1800Z 18.1N 114.8W   40 KT  45 MPH
 24H  14/0600Z 18.8N 116.4W   45 KT  50 MPH
 36H  14/1800Z 19.4N 118.0W   50 KT  60 MPH
 48H  15/0600Z 19.9N 119.4W   55 KT  65 MPH
 60H  15/1800Z 20.5N 120.7W   55 KT  65 MPH
 72H  16/0600Z 21.2N 122.0W   55 KT  65 MPH
 96H  17/0600Z 22.0N 124.5W   45 KT  50 MPH
120H  18/0600Z 22.0N 127.0W   30 KT  35 MPH
 
$$
Forecaster Beven
 
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