Weather is inherently unpredictable. They'll never be perfect.
I missed the most important point: because the economy is made up of intelligent actors - there is a dynamic aspect to economist predictions.
If the weatherman says 'it will be 'very hot' next week' - this can be right or wrong, but the weather won't change as a result.
If a prominent economist says 'there will be a recession next month' - business leaders may hold up on investment thereby causing a recession, where none might have been.
So it's pretty hard to predict the future, when your predictions change the future ;)
weather forecasts have been getting more and more accurate, actually