If we are lucky Hurricane Lee will harmlessly develop into a major category 4 or 5 hurricane as it passes north of Puerto Rico and the islands of the Caribbean over the next week, then shoots the gap between Cape Hatteras and Bermuda before recurving back out into the open north Atlantic east of the Canadian maritime provinces between ten days and two weeks from now. Let us pray for nothing but surf, because all the models and the National Hurricane Center are predicting that Lee will become a monster. Let’s be clear that all of the models are in good agreement about the next 5 days and there’s good confidence in the NHC forecast track that takes Lee safely north of Puerto Rico. It’s possible that the weak side of Lee could affect one of the Lesser Antilles, but the Caribbean looks pretty safe. The uncertainties build quickly after the end of the NHC’s 5 day forecast. The problem is that Lee will likely be a major category 4 hurricane or higher in five days.
The combination of low wind shear and record sea surface temperatures and heat in the upper ocean will turn Lee into an extremely dangerous storm.
This morning’s NHC tropical storm Lee discussion is the first time I have ever read a NHC forecaster use the term “explosive intensification” in a discussion. The earth’s energy imbalance has doubled over the past 2 decades and the oceans have taken up 90% of the heat that is not radiating back out to space. The tropical and subtropical north Atlantic is one of the oceanic regions where the heat is concentrating. That ocean heat uptake has consequences and one of them is the increasingly rapid intensification of tropical storms and hurricanes when they have ideal low wind shear conditions.
NHC tropical storm Lee discussion excerpt for 5am 6Sept23.
Lee has already been strengthening fairly quickly despite someeast-northeasterly vertical wind shear over the system. Since the shear is expected to relax while the storm remains over very warm water and in a moist environment, continued steady to rapid intensification is expected during the next few days. Most of the intensity models are very aggressive, bringing Lee to major hurricane status by the weekend, but they don't show much change in strength in the short term. In addition, even the global models like the GFS and ECMWF show explosive intensification and forecast Lee's minimum pressure to drop by more than 60 mb by the end of the forecast period. The NHC intensity forecast lies near the high end of the model guidance during the next 24-48 hours, but falls to near the middle of the guidance envelope after that. Regardless of the details, there is high confidence that Lee will be a powerful hurricane late this week and over the weekend.
This year every ocean basin in the northern hemisphere has had more accumulated cyclone energy than normal. El Niño years typically increase hurricane activity in the Pacific ocean, and decrease activity in the Indian and North Atlantic ocean because they involve the release of stored hot water into the equatorial eastern Pacific ocean. This year is different. It is so hot that the increased wind shear from the Pacific is not holding storm activity down. By mid June the tropical north Atlantic had so much heat build up that it became clear to me that this hurricane season would be exceptionally active, despite El Niño.
www.dailykos.com/...
Microwave imaging cuts through the high clouds that can obscure the inner structure of hurricanes. Microwave imaging taken at 21 hours GMT — 5pm eastern daylight time — shows Lee had developed an eye.
Noon 7Sept23 Update: The explosive intensification I wrote about yesterday afternoon got serious this morning. The NHC upgraded Lee to category 2 at 105mph (90kts) this morning and it will likely be category 4 on tonight’s advisory based on the satellite signature of a very warm eye and very cold cloud tops above the eyewall. The NHC forecasts Lee’s sustained winds to be 115kts (130 mph) at 11 EDT tonight but the present satellite signature at noon today indicates that their prediction may be a little conservative. The official forecast brings Lee to category 5 at 160mph in 36 hours, tomorrow evening.