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Tropical Storm Isaac Discussion Number   1
NWS National Hurricane Center Miami FL       AL102024
1100 PM AST Wed Sep 25 2024
 
The non-tropical area of low pressure we have been monitoring to the 
northeast of Bermuda over the last day or so has become 
significantly better organized today, with deep central convection 
forming and now wrapping around a small surface circulation. While 
the system had previously been attached to an occluded frontal 
boundary to its northwest, recently received scatterometer data now 
shows that the circulation has fully detached form this boundary, 
and is producing winds of 40-45 kt in a small circular area embedded 
within the organizing convection. These structural changes indicate 
the the system has undergone and has completed tropical 
transition. Thus, the system is now being designated Tropical Storm 
Isaac this advisory, and the initial intensity is set to 45 kt based 
on the earlier scatterometer data.
 
Isaac is moving just north of due east at 85/10 kt. This motion 
should continue with a gentle turn more east-northeastward over the 
next several days as the system is steered primarily by mid-level 
ridging present to its south. However, there does not appear to be a 
mid-latitude trough early on to help the storm to accelerate much 
over the next few days. The initial NHC track forecast is in good 
agreement with the simple and corrected consensus aids TCVN and 
HCCA.
 
While Isaac is traversing only marginally warm waters, it is also 
still embedded within the base of an upper-level trough which has 
reduced tropospheric stability due to colder upper-level 
temperatures. This is partially why Isaac has been able to develop 
organized deep convection this evening. The shear is not 
anticipated to increase much over the next couple of days, which 
could allow for some gradual intensification. The NHC intensity 
forecast is in good agreement the with HCCA and ECMWF forecasts and 
shows a peak intensity of 60 kt in 48 h, followed by gradual 
weakening after 72 h as sea-surface temperatures cool further and 
shear begins to increase more markedly.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0300Z 37.1N  54.1W   45 KT  50 MPH
 12H  26/1200Z 37.1N  52.3W   50 KT  60 MPH
 24H  27/0000Z 37.3N  49.8W   50 KT  60 MPH
 36H  27/1200Z 37.9N  46.8W   55 KT  65 MPH
 48H  28/0000Z 38.8N  43.2W   60 KT  70 MPH
 60H  28/1200Z 40.1N  39.5W   60 KT  70 MPH
 72H  29/0000Z 41.4N  35.8W   60 KT  70 MPH
 96H  30/0000Z 42.7N  29.4W   55 KT  65 MPH
120H  01/0000Z 42.5N  21.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Papin
 
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