The final advisory was just written on Joaquin last night as it transitioned to an extratropical cyclone, so I'll go over its fairly unique evolution. Joaquin's origins could be traced all the way back to around September 17-18 as an upper-level low pressure system. While tropical development from upper-level "cold core" lows is not unheard of, it is rare for storms of that pedigree to become nearly Category 5 hurricanes. Here is a quick timeline as a recap:
Sept 18: upper-level low identifiable
Sept 25: becomes disturbance of interest, or "Invest"
Sept 28: upgraded to tropical depression
Sept 29: upgraded to tropical storm
Sept 30: upgraded to hurricane
Oct 1: upgraded to major hurricane
Oct 3: strengthens to 135kts, just short of Category 5 status
Oct 7: weakens to tropical storm
Oct 8: final advisory written as extratropical cyclone
|Water vapor images at select milestones in Joaquin's lifecycle leading up to its peak intensity.|
|Average seasonal cumulative ACE (purple) and 2015's accumulation so far (yellow).|
Recent October hurricanes that reached Category 4-5 intensity are:
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