129  WTNT43 KNHC 242057 TCDAT3  Hurricane Sam Discussion Number   9 NWS National Hurricane Center Miami FL       AL182021 500 PM AST Fri Sep 24 2021  Sam's structure on satellite has improved this afternoon, with  overshooting cloud tops rotating quickly around the small central  dense overcast, providing the appearance that the hurricane is  mixing out the dry air that affected its core structure this  morning. In fact, the last few visible satellite images suggest that  a small eye is clearing out within the cirrus canopy. Interestingly,  a recent 1930 UTC SSMIS pass suggests concentric bands are also  forming in Sam's core structure and it remains to be seen how that  structure will affect the wind field evolution of the hurricane. The  latest subjective Dvorak intensities estimates form TAFB and SAB  were a consensus T4.5/75 kt, while the latest SATCON and ADT  estimates from UW-CIMSS have also increased this afternoon. The  current advisory intensity has been set to 75-kt. Given the  recent trends on satellite, this may be conservative.  The motion of Sam has remained on the same heading, though the storm is beginning to slow down with the estimate now at 280/10 kt. An additional slowdown in forward motion is anticipated in the short-term as the mid-level ridging shuffles to the northwest of the tropical cyclone, impeding its forward motion. However, after  72 hours, this same ridge is expected to shift back to the  northeast of Sam as a deep-layer trough off the Eastern United  States coastline becomes established. Track guidance spread  increases towards the end of the forecast, with the ECMWF and GFS  remaining at odds, with the former on the equatorward side, and  the latter on the poleward side of the track envelope. The  consensus aids, however, have changed little from the previous  advisory and the latest NHC track forecast is quite similar to the  previous one.   Now that Sam appears to have mixed out the dry air seen this  morning, intensification, likely rapid, is resuming. The only fly in  the ointment is the current concentric banding structure on  microwave imagery, which hints at the possibility of an eyewall  replacement cycle. Assuming the smaller eye will not collapse in the  short term, rapid intensification appears likely over the next 12-24  hours and the intensity has been raised in the short term, taking  Sam to major hurricane intensity by tomorrow. The latest NHC  intensity forecast now shows a slightly higher peak at 120-kt in 48  hours followed by very gradual decay, due to a subtle increase in  vertical wind shear, potentially some upwelling effects due to the  slow forward notion, and eyewall replacement cycles that could lead  to a broadening of the wind field. The latest NHC intensity forecast  starts out on the high side of the intensity guidance but ends up  very close to the HCCA consensus aid by the end of the forecast  period.  Regardless of the details, Sam is expected to be a  significant hurricane through the forecast period.   FORECAST POSITIONS AND MAX WINDS  INIT  24/2100Z 12.1N  44.8W   75 KT  85 MPH  12H  25/0600Z 12.3N  46.5W   90 KT 105 MPH  24H  25/1800Z 12.7N  48.1W  105 KT 120 MPH  36H  26/0600Z 13.1N  49.3W  115 KT 130 MPH  48H  26/1800Z 13.5N  50.5W  120 KT 140 MPH  60H  27/0600Z 14.3N  51.7W  115 KT 130 MPH  72H  27/1800Z 15.1N  52.9W  115 KT 130 MPH  96H  28/1800Z 16.9N  55.1W  110 KT 125 MPH 120H  29/1800Z 18.9N  58.1W  110 KT 125 MPH  $$ Forecaster Papin