Some have asked if Ida becoming a hurricane this morning was a surprise. I can’t speak for the National Hurricane Center (NHC) forecasters, but I suspect they would say that it takes a lot to really surprise them. The NHC Hurricane Specialists issue forecasts on over 25 tropical cyclones each year if you combine the Atlantic and east Pacific basins for which they have responsibility. These forecasters have seen a lot of erratic behavior when it comes to tropical cyclone tracks and a lot of rapid changes in intensities. They understand very well the uncertainty in forecasting.
When the initial advisory was issued on Tropical Depression Eleven at 10:00 am EST on Wednesday, November 4th, there was a 10% probability of it becoming a hurricane within 24 hours based on the Intensity Probability Table issued with that advisory. The probability of Tropical Storm Ida becoming a hurricane within 12 hours had increased to 17% based on the 10:00 pm EST Wednesday, November 4th advisory. These probabilities were low, but certainly not zero.
Based on Air Force reconnaissance data received after the 4:00 pm EST advisory was issued yesterday, the maximum sustained winds were increased to 65 mph at 5:30 pm EST. That is only 9 mph short of hurricane force winds. The public advisories mentioned that Ida could approach hurricane intensity before making landfall although the forecast did not explicitly forecast a hurricane. The Hurricane Watch for the coast of Nicaragua that was coordinated between NHC and the National Meteorological Service of Nicaragua and issued near 5:30 pm EST yesterday meant that there was a possibility of hurricane conditions within the watch area.
To me, the take-away lesson from Ida so far is that we have yet another reminder that the forecasts are not perfect. The sooner we learn to accept that uncertainty is a fundamental characteristic of weather forecasting and that no forecast is complete without a description of that uncertainty, the better off we will be.