Tropical Storm Isaac Discussion Number   5
NWS National Hurricane Center Miami FL       AL102024
1100 PM AST Thu Sep 26 2024

Isaac's structure has quickly improved this evening on satellite 
imagery. Deeper cold convection down to -60 C has been fully 
wrapping around the center, and the last few frames show a warm 
spot, which could very well be a formative eye. While the 
subjective Dvorak classifications hasn't changed much this evening, 
the objective estimates, especially DPRINT and DMINT from UW-CIMSS 
have increased to 54 and 51 kt respectively. Similar to last night, 
a late arriving set of scatterometer passes showed a tight vortex 
with derived-winds up to 49 kt. Assuming some undersampling of the 
small circulation, the initial intensity is raised to 55 kt this 
advisory. 

Isaac appears to have made a wobble south of due east earlier this 
evening, but more recently has resumed an eastward motion at   
90/10 kt. This motion with a gradual turn to the east-northeast 
should occur over the next couple of days. Afterwards, the forward 
motion of Isaac is likely to become very critical to its future 
track trajectory. The poleward shift in the guidance that started 
earlier today has continued, possibly due to the slower forecasted 
forward motion of the storm, making it more likely to be captured by 
an upstream mid-latitude trough digging in from the west. The latest 
NHC track forecast has continued the northward shift started on the 
prior cycle, but is still not as far north and east as the bulk of 
the guidance suite, and further adjustments in that direction may be 
needed in future forecasts. 

Given the improvement in Isaac's structure this evening, it's 
looking increasingly likely the storm will soon become a hurricane. 
Vertical wind shear remains under 20 kt while sea-surface 
temperatures (SSTs) between 26-27 C for the next 24 h should allow 
additional intensification. After that time, shear begins to 
increase more as SSTs also begin to cool. These factors are expected 
to result in a leveling off in intensity, though cold upper-level 
temperatures should maintain enough instability to keep moderate to 
deep convection near the system. By 72 h, weakening should begin, 
with extratropical transition likely to be underway, finishing 
sometime early next week over the high-latitudes of the North 
Atlantic. The latest NHC intensity forecast is above much of 
the guidance in the short-term due to recent satellite trends, but 
falls back towards the reliable HCCA consensus aid after 24 hours.


FORECAST POSITIONS AND MAX WINDS

INIT  27/0300Z 37.1N  49.8W   55 KT  65 MPH
12H  27/1200Z 37.1N  47.6W   65 KT  75 MPH
24H  28/0000Z 38.1N  44.1W   70 KT  80 MPH
36H  28/1200Z 39.5N  40.5W   70 KT  80 MPH
48H  29/0000Z 41.1N  37.9W   65 KT  75 MPH
60H  29/1200Z 42.6N  36.4W   65 KT  75 MPH
72H  30/0000Z 43.7N  35.1W   60 KT  70 MPH
96H  01/0000Z 46.0N  30.4W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  02/0000Z 50.0N  26.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin