Likely: Well Into August Before Deep Tropics Cyclone in North Atlantic

Madden Julian Oscillation Shuts Down Atlantic Deep Tropics
07/18/2018, 4:18 pm EST
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07/27/2018, 9:24 am EST
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Lack of support for activation of the deep tropics next 2-4 weeks

Fig. 1: Morning IR satellite view of the North Atlantic basin.

Discussion: Later in July it’s natural for an area of convection to emerge in the deep tropics of the North Atlantic basin. Signs of the Intra-tropical convergence zone (ITCZ) have evolved the past few days although convection is very weak and disorganized due to cooler than normal sea surface temperature anomalies (SSTA) and attendant below normal upper ocean heat plus an unfavorable atmospheric environment caused by the subsidence phase of the Madden Julian oscillation (MJO).

Upper shear continues to arc across the Caribbean Sea voiding any tropical wave development in that region which is not unusual for late July. The persistence of the upper shear is somewhat related to the El Nino-like convection upstream across the tropical East Pacific. Although El Nino has not formed the multivariate ENSO index (MEI) indicates the past 2 months the atmosphere has been in a borderline El Nino climate. (MEI measures the atmospheric reaction of equatorial Pacific temperature and sea level pressure anomalies).

The subtropics are producing areas of potent thunderstorm activity mostly due to cold core upper troughs moving over very warm ocean water. Thunderstorms off the Southeast U.S. Coast will be entrained into an eastern U.S. frontal zone causing flash flooding subtropical rains from the Mid-Atlantic to Northeast U.S. the next 2-3 days. An area of thunderstorms associated with an upper trough near Bermuda is unlikely to develop due to high surface pressure associated the “Bermuda High”.

Operational models indicate no tropical issues through the next 1-2 weeks.

The convection phase of the Madden Julian oscillation rests in the tropical West Pacific/Maritime Continent helping to enhance the wet monsoon season. MJO presence in the West Pacific has spawned several tropical systems. The MJO forecast is weakening presence in the West Pacific over the next 2 weeks. The less focused convection in the West Pacific during early August may lend assistance to evolving ITCZ-style convection in the East Pacific in early August to inspire a more active tropical pattern. However, large-scale support to activate the tropical North Atlantic is poor for the next 2-4 weeks.

Fig. 2: The 15-day Madden Julian oscillation forecast provided by Storm Vista WX Models indicates West Pacific presence (now) fades the next 1-2 weeks.