Fig. 1: The convection phase of the Madden Julian oscillation stretches across Indonesia enhancing tropical cyclone risk. The subsidence phase is located across the North Atlantic tropics where skies are mostly clear.
Discussion: The Madden Julian oscillation (MJO) is an excellent predictor of where greatest risk of tropical cyclone development is likely to occur across the tropical oceans. Tropical systems forming in the subtropics, pole ward of the deep tropics can form without help from the MJO. Currently, the convection phase of MJO stretches across Indonesia where widespread heavy thunderstorms are located. The MJO has been stuck in this region for a while and responsible for excessive rainfall produced by the Southeast Asia Monsoon the past 2-3 weeks.
The subsidence phase of the MJO is down wind centered on the tropical North Atlantic basin. In this zone sinking air motion is suppressing convection and preventing tropical waves from forming. Upper westerly shear is also present often found down wind of heavy convection in the tropics.
The ECMWF 30-day MJO forecast indicates only a slight eastward shift of the MJO into the tropical West Pacific. The model also indicates the MJO signal weakens. The forecast implies support for tropical cyclone development to the east, certainly in the North Atlantic tropics is minimal as the subsidence phase of the MJO continues possibly well into August.
Ideally, MJO presence centered on the far eastern tropical North Atlantic to the far western tropical Indian Ocean producing convection that can ignite strong tropical waves moving off the Africa Coast and into the North Atlantic tropics is the classic process to generate hurricanes. However, this scenario is unlikely well into August which is not unusual.
Hybrid tropical systems forming from clusters of thunderstorms moving off the U.S. Gulf or East Coast generated by frontal zones are possible independent of the MJO. Two areas for this possibility are being monitored in the northeast Gulf of Mexico and off the Carolina Coast at this time.