With significant external threats to NOAA, I figured it may be pertinent to discuss what TC forecasting looked like a mere half century ago. All images used in this thread come from the NHC — I will be focusing on 1974’s Hurricane Fifi, at 00z on September 19th. 1974 was an important year in operational TC forecasting because it was the first where some version of the Dvorak technique was available to aid in estimating hurricane strength. It was pioneered by Vernon Dvorak the previous year and was simpler than the modern version.

The West African monsoon trough has just about reached its climatological maximum latitude, peaking at about 20N in northern Mali/central Mauritania. The eastern extension of this feature is abnormally far north, at similar latitudes of Chad and Sudan.



As far as Atlantic tropical cyclone activity goes, this has two byproducts. Firstly, enhanced convection over the Sahel region leads to more robust tropical waves, which tend to hold together better as they roll off of Africa and into the Atlantic.

[Thread]: As a result of weak or reversed trade winds, a broad gyre-like feature has become established over the eastern MDR. Vorticity maxima that form within this have generally rotated around the periphery into a more stable environment to the north. These features aren’t necessarily uncommon in during this time of the year. Different speeds of heating between the Atlantic and Africa favor a NE to SW tilt to the monsoon trough, which tends to break off into these cyclonic gyres that drift west in weak trade winds.

There’s been a lot of talk about TS Ida passing over an eddy that separated from the Loop Current while it’s traversing the Gulf of Mexico. Many of these tweets refer to the associated high oceanic heat content, and it’s worth taking a look at how and why this may be important. The first question to address: What is OHC and TCHP? Oceanic heat content (or OHC) is the vertical integration of heat in the ocean. It’s a rather general term that enjoys widespread usage. For TC purposes, only the upper ocean is considered (above the 26C isotherm).

Past studies on African Sahel rainfall (including analysis of past droughts late in the 20th century) have indicated that the precipitation in the region has a decent correlation to the interhemispheric temperature gradient. The aforementioned extreme drought in the latter half of the 20th century can be explained by this mechanism, with warming in the Southern Hemisphere outpacing that of the Northern half of the globe. It’s likely that this is a fault of anthropogenic causes, with human emissions…