Wave off Cape Verde likely to become depression, Tropical Storm Fred

I made a great forecast.  I just didn’t post-date it.  But, you knew what I was talking about anyway, didn’t you?  The NHC designated a Cape Verde wave Invest 96L yesterday.  The wave was impressive coming off Africa.  But, traumatized from my reaching-out-on-a-breaking-limb experience, I wasn’t about to get involved.  So, here I am.  Late to the game but ready to bat.  Put me in, coach (don’t ask about the baseball references – I’m a Texans fan).

Upper-Air Analysis

Invest 96L is currently under an upper-level anticyclone with winds 5-10kts; very favorable for convection and divergence.  This anticyclone is forecast to follow the system for the next few days until weakening allowing stronger upper-level wind shear to tear apart the storm – provided that the storm makes a gradual northwestward turn in a couple of days.

Satellite trends from the sporadic Meteosat showed the 1007mb low had most of the convection to the north and west of the wave axis.  Currently, outflow is restricted to the northwest quadrant of the system.

IR imagery from earlier this morning showed there were some cloud tops pushing -80°C but they were located well away from the wave axis to the northwest.  As with all developing tropical cyclones, expect this type of convection to develop over the wave axis or for a surface circulation to develop beneath the existing convection.

The wave also has a great amount of Saharan dust to the north of the system and, while this could be an issue as the system gains latitude, it shouldn’t be enough to prevent near-term development.

The wave is also surrounded by a good deal of atmospheric moisture.  However, should the storm take the northwestward turn lack of moisture will aid in weakening the system and likely prevent it from becoming a hurricane.  If the system continues west-northwest as predicted by the GFS Ensemble (see below), there is more moisture available for the storm to work with – more energy – and a greater likelihood of becoming a hurricane.

Forecast

Several models are forecasting the wave to make a gradual turn towards the west-northwest within a couple of days in response to a weakening ridge to the north.  As this ridge weakens, shear is expected to increase over the system and begin a permanent weakening trend.

Interestingly, however, the GFS Ensemble mostly keeps the wave moving west-northwest throughout the next five days.  The GFS has had issues this year handling developing systems and weakening ridges.  I think at this time since most of these models are outliers they should be temporarily disregarded.  I am a bit cautious to do that as the earlier run did essentially the same output.  If these models continue to go about this route, however, they should be given more weight for, if anything, consistency.  I should also note that I know these models are taking the output from other models in regards to surrounding atmospheric features.  I do not know what models they are feeding off which would give me more confidence in discrediting or recognizing their output.  So, I’m basically flying blind here.  My tendency is to always exercise caution when the GFS Ensemble goes about different forecasts from other models – at least, drastic differences such as this.

Invest 96L is not expected to become a hurricane at this time and this is purely based upon the fact the same models are anticipating a northward turn.  If the wave does not make this turn or not as soon as forecast, it is more likely the system could attain hurricane status.  However, rapid intensification is definately out of the question as of this time.

Sea Surface Temperatures and Oceanic Heat Content

SSTs in front of 96L are favorable for development.  However, as you can see in the map below, if the storm does turn north it will soon run out of favorable ocean temperatures.  If the wave continues on a west-northwest track as predicted by the GFS Ensemble, water temperatures will remain at a minimum for tropical cyclone development, but not low enough to induce weakening.  This is highly dependent on the path the storm takes, of course.

Regardless of where the wave tracks, oceanic heat content will remain at a minimum thus nearly eliminating the risk of any rapid intensification trends.