ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Blanca Discussion Number 9 NWS National Hurricane Center Miami FL EP022021 300 PM MDT Tue Jun 01 2021 Over the last 12 h, Blanca's convective structure has continued to degrade. The low-level circulation center is now fully exposed to the west of a small region of deep convection, though disorganized convective towers are currently trying to redevelop closer to the center. Even though deep-layer southwesterly 200-850-mb vertical wind shear diagnosed by GFS-SHIPS is still only 15-20 kt, stronger 25-30 kt mid-level shear appears to be undercutting Blanca's outflow layer. This shear may have resulted in Blanca ingesting dry, stable mid-level air from the west that has significantly disrupted the cyclone's convective structure today. Unfortunately all three scatterometer passes missed Blanca's center and maximum winds this afternoon. However, given the marked decrease in organization of Blanca's structure, plus recent subjective satellite estimates from SAB and TAFB at T3.0/45 kt, the initial intensity has been lowered to 45 kt for this advisory. Blanca's exposed center has made it easier to determine its current position and motion, which over the past 12 h is estimated at 300/8 kt, though the shorter-term motion has been more westward. As previously discussed, the mid-level ridge that had been steering Blanca to the west-northwest has been gradually weakening as a pronounced mid- to upper-level trough centered over the Baja California peninsula digs in. The end result is Blanca's forward motion toward the west-northwest is likely to slow further. Additional asymmetric convective bursts primarily occuring east of the low-level center may also act to slow down Blanca's forward motion. As the storm becomes more vertically shallow, it will increasingly be influenced by the low-level steering flow resulting in a gradual westward bend in the forecast track until Blanca dissipates. The latest NHC forecast track has shifted a bit more south and west this cycle, owing to the possibility that Blanca may become a shallow vortex sooner than expected, but still agrees closely with the HCCA corrected consensus with a little more weight placed on the leftward bending guidance. The same mid- to upper-level trough slowing the steering currents have also resulted in a significant increase in mid-level shear over Blanca, halting any further intensification. Over the next 12-24 h, intermittent diurnal convective bursts as the cyclone remains over 28-29 C sea surface temperatures should lead to only gradual weakening. However, even drier mid-level air and lower sea-surface temperatures exist along Blanca's forecast track and the cyclone is forecast to weaken to a tropical depression by 60 h and degenerate to a remnant low by 96 h, though this could occur sooner if organized convection dissipates faster than forecast. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 14.7N 110.9W 45 KT 50 MPH 12H 02/0600Z 15.0N 111.6W 40 KT 45 MPH 24H 02/1800Z 15.4N 112.3W 40 KT 45 MPH 36H 03/0600Z 15.6N 112.9W 35 KT 40 MPH 48H 03/1800Z 15.7N 113.5W 35 KT 40 MPH 60H 04/0600Z 15.7N 114.4W 30 KT 35 MPH 72H 04/1800Z 15.8N 115.5W 30 KT 35 MPH 96H 05/1800Z 15.9N 117.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 06/1800Z 15.9N 119.2W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Papin/Stewart NNNN