Forecasters raise the hurricane season outlook, and explain why the number of storms is the least useful part

Forecasters have raised their seasonal outlook to 17 to 21 named storms, of which 8 to 11 are expected to reach hurricane strength. The revision reflects two conditions that have both moved in the same direction: unusually warm sea surface temperatures across the main development region, and wind shear forecast to remain weaker than normal through the peak.

Warm water supplies energy; low shear allows a young storm to organize instead of being torn apart. When both align, more disturbances become named storms.

The number that does not help you

Emergency managers have spent years asking forecasters to de-emphasize the seasonal count, and forecasters largely agree with them.

A season with 21 storms that all recurve into open ocean does less damage than a season with 8 in which one crosses a populated coast at category four. The count measures activity in the basin. It does not measure risk to any particular place, and the correlation between the two is weak.

The season total is a fine number for a scientist and a useless one for a family deciding whether to buy shutters.— A county emergency management director

What to do with a seasonal outlook

The practical use of a busier-than-normal outlook is as a prompt for preparation that takes time: reviewing an insurance policy, which typically has a 30-day waiting period for flood coverage; confirming evacuation zone and route; and replacing supplies that expired since last season.

None of that depends on knowing how many storms form. All of it becomes impossible in the 48 hours before a landfall, when it is most obviously needed.

• Outlook: 17 to 21 named storms; 8 to 11 hurricanes
• Drivers: warm sea surface temperatures and forecast weak wind shear
• Limitation: seasonal counts carry no information about landfall location
• Flood insurance: typically a 30-day waiting period before coverage begins

Peak activity in the basin runs from mid-August through early October. Forecasters will update the outlook once more before the peak, and stressed that a downward revision would not be a reason to relax preparations that are useful regardless of the count.