Tropical Depression Blanca Forecast Discussion Number 13

NOAA - Tropical Weather Updates

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Issued at 300 PM MDT Wed Jun 02 2021

WTPZ42 KNHC 022037
Tropical Depression Blanca Discussion Number  13
NWS National Hurricane Center Miami FL       EP022021
300 PM MDT Wed Jun 02 2021
The satellite structure of Blanca has continued to deteriorate this 
afternoon. Visible satellite imagery shows an exposed low-level 
swirl, and that circulation is becoming increasingly elongated. The 
nearest deep convection is now more than 100 nm southeast of the 
circulation center. A fortuitous 1519 UTC ASCAT-A pass over Blanca 
revealed that the tropical cyclone may have been weaker than earlier 
assessed with a peak wind retrieval of only 28 kt in the 
northeastern quadrant. Even after accounting for instrument 
undersampling, the lack of significant convection near the wind 
field since that time has likely resulted in further spin down of 
the vortex. The latest subjective Dvorak estimates were also down 
to 30 kt from SAB and 35 kt from TAFB. Given the deterioration of 
the structure since then, Blanca is being downgraded to a 30-kt 
tropical depression at this time.

As Blanca's low-level circulation has become increasingly detached 
from the deep convection, the motion of the storm has turned more 
westward at 280/4 kt. Now that Blanca appears to be a shallow 
low-level feature, it will be primarily steered by the low-level 
easterly trade wind flow. This will force Blanca westward over the 
next several days as the circulation slowly spins down. The latest 
NHC track forecast is largely an update from the previous one and 
remains closest to the HCCA consensus model which is on the left 
side of the guidance envelope.

Aside from the limited deep convection well separated from Blanca's 
center, the storm already barely meets the criteria of a tropical 
cyclone. It appears that dry, stable air that entered the 
circulation from the northwest, aided by unfavorable vertical wind 
shear, is winning the battle over sufficiently warm sea-surface 
temperatures beneath the circulation. With the wind field spinning 
down compared to 24 h ago, nocturnal re-formation of deep central 
convection will find it more challenging to overcome the dry stable 
airmass that the storm is embedded in. In addition, both the 12z 
GFS- and ECMWF-model-forecast simulated IR brightness temperature 
have trended towards less convective activity the last few cycles. 
The current NHC forecast assumes occasional diurnal convective 
bursts will help to maintain the status of the tropical cyclone for 
another 24-36 h, but it is possible that Blanca could become a 
remnant low as soon as tomorrow afternoon if convection does not 
redevelop by then. 
INIT  02/2100Z 15.5N 112.8W   30 KT  35 MPH
 12H  03/0600Z 15.5N 113.4W   30 KT  35 MPH
 24H  03/1800Z 15.4N 114.2W   30 KT  35 MPH
 36H  04/0600Z 15.3N 115.5W   25 KT  30 MPH
 48H  04/1800Z 15.2N 117.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  05/0600Z 15.2N 118.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  05/1800Z 15.2N 119.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  06/1800Z...DISSIPATED
Forecaster Papin/Stewart

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