Hurricane Helene in the Yucatan channel 11am Cuban time Sept 25
Helene has just become a hurricane near Cozumel Mexico in the Yucatan channel which is the portal of passage for hurricanes entering the Gulf of Mexico from the Caribbean. Helene has mixed out dry air that entered from the west and Cuban radar shows that the break in the eyewall on the southeastern side is closing. Wind shear has dropped off as an upper level low to the northwest has broken down, in part, because of the strong outflow from Helene. The sea surface temperatures on Helene’s forecast track are 86ºF (30Celsius) or higher until very close to projected landfall. Much of the forecast track is over or near the very warm, very deep, loop current. The National Hurricane Center is forecasting Helene to rapidly intensify to a major hurricane of 125 mph (110knots) before landfall. That’s a strong category 3. That’s the experts’ best forecast at this time.
5pm Update: In 24 hours the NHC forecasts that Helene will be a category 4 hurricane.
24H 26/1800Z 27.4N 85.2W 115 KT 130 MPH
Be prepared for it.
Official NHC forecast cone for hurricane Helene issued at 11am EDT Sept 25. Helene is forecast to make landfall in Florida in the big bend region or the Florida panhandle. Extreme storm surges are expected in the big bend region.
The problem forecasters face is that climate change is primarily the result of the oceans taking up enormous amounts of heat because greenhouse gases have reduced the amount of heat that the oceans are radiating out to space. The earth has a radiation imbalance and the oceans are taking up about 90% of the heat involved in that imbalance. The tropical North Atlantic ocean and the Gulf of Mexico are two of the regions that have taken up large amounts of heat in response to greenhouse gas emissions. Hurricanes derive their power from stored ocean heat. As storms intensify the stir up cold water from below if there is cold water in the upper ocean. The heating of Gulf and North Atlantic ocean caused by the radiation imbalance means that warm water is found deeper in the ocean which means that hurricanes have the potential to get stronger than they would have fifty years ago given similar surface temperatures and atmospheric conditions. Hurricanes today are more likely to intensify explosively to category 4 or 5 than fifty years ago. This makes hurricane forecasting and emergency planning a nightmare in a situation like the one we have right not with Helene. The HFS-B model run from this morning forecasted a strong category 5 hurricane with 155kt (180mph) winds just before landfall. This forecast is in the realm of possibility.
Hurricane Helene's forecast track midday Sept 25 overlain on ocean heat content. Helene will pass over or near the deep very warm Loop current for most of it's forecast track.
As horrific as this morning’s HFS-B model run was, it’s not the worst case given today’s Gulf of Mexico sea surface temperatures and ocean heat content. The worst case is a hurricane of over 175kt — over 200mph — sustained winds. That’s the sustained wind speed that the ocean heat could (approximately) potentially provide to spin up the hurricane.
The maximum potential hurricane intensity for Helene is greater than 175 knots (200mph)
Forecasters have to make their best expert judgments to predict the size and intensity of a hurricane based on large data sets and a range of forecast model outputs. Predicting the intensity of a hurricane continues to be one of the hardest aspects of hurricane forecasting. The forecast models have greatly improved predictions of hurricane tracks over what they did a few decades ago.
Rapid intensification is perhaps the most challenging problem facing hurricane forecasters. Hurricane Helene is set to intensify rapidly now that the eye wall is closing, shear is low and ocean heat is high. The problem forecasters face is how rapidly and how intense will it get. Model outputs have been extremely variable between models and between model runs of the same model at different initialization times. The forecasters use their best judgment to integrate all of the information to give us their forecasts, but climate change has made it a nightmare because the worst case has become so extreme. The Pacific hurricane that went far south of Lahaina, Maui, and the extreme Pacific high pressure area to the storm’s north were more intense than the worst case potential model. I watched the satellite loops wondering WTF before the winds hit Maui. That was a nightmare far worse than I imagined when I looked at the hurricane and north Pacific wind forecasts. No forecaster wants to be involved in that kind of situation. I’m glad that I don’t have to be a forecaster at the NHC predicting the intensity of Helene just before landfall.
