Issued at 300 PM MDT Wed Jun 02 2021
000 WTPZ42 KNHC 022037 TCDEP2 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. FORECAST POSITIONS AND MAX WINDS 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
