Tropics Will Activate But Just How Much?

European Model: 3 Tropical Events North Atlantic Next Wednesday
08/29/2018, 1:36 pm EDT
North Atlantic To Become Active – But Less Active Than Previously Forecast
08/30/2018, 8:59 pm EDT
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The largescale environment of the tropical/subtropical North Atlantic is forecast to improve during the first third of September for tropical cyclone development. However, the catalyst for improving the North Atlantic tropical environment is trending less robust.

 Pulling back the reigns

NHC initiates statements on “potential tropical cyclone 6” at 11AM

Fig. 1-2: The NCEP and ECMWF 14-day MJO forecast indicate support of enhancement for tropical cyclone risk is now tilted more toward the East Pacific rather than the North Atlantic.

Discussion: The most recent Madden Julian oscillation forecast by both NCEP and ECMWF operational models (Fig. 1-2) indicate the summer-long presence in the tropical West Pacific shifts east in early September. However, the eastward shift is to the East Pacific tropics and less so the Atlantic tropics (versus previous forecasts). This (MJO forecast) change is extremely important regarding influence on the North Atlantic tropics the next 1-2 weeks.

The upper shear pattern across the North Atlantic (Fig. 2) remains strong enough to prevent tropical wave/tropical cyclone development. The MJO presence in the North Atlantic tropics is required to completely ease the shear pattern. It’s possible the shear continues with an active East Pacific tropics.

Fig. 2: The upper shear axis analysis across the North Atlantic basin.

Presence of the upper shear causes forecast models to bend Florence northward once reaching the central subtropical North Atlantic mid-to-late next week (Fig. 3). Tropical cyclone models indicate Florence will emerge within 1-2 days and travel to the central tropical North Atlantic in 5 days (Fig. 4).

Also note the tropical wave near Puerto Rico emerging despite presence of upper shear. This system will migrate slowly west-northwest likely reaching the Gulf of Mexico Tuesday then inland Louisiana midweek. Proximity to land during travel of this system implies a tropical cyclone is unlikely.

Fig. 3: The North Atlantic satellite view.

Fig. 4: Tropical cyclone models 5-day forecast track of 90L.