MJO Causes Record Slow Start to West Pacific TC Season

Precedent for North Atlantic TC Season When Main Development Region for Hurricanes is Much Warmer than Normal in June
07/14/2020, 11:18 am EDT
Tracking Peak of Summer Heat Waves
07/19/2020, 11:58 am EDT
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Fig. 1-2: The MJO stalls in the western tropical Indian Ocean in June/July (so far) and the 2-week forecast indicates very little change.

Discussion: The Pacific tropical basin has observed no significant tropical cyclone activity since early June including no category-3 systems, the first time in the satellite measuring era (since 1966) according to the Australia Bureau of Meteorology. Using accumulated cyclone energy (ACE) index the seasonal activity (so far) for the Pacific basin is 20% of normal. The catalyst to this pattern is a stalled convection phase of the Madden Julian oscillation in the western tropical Indian Ocean. East of the MJO pattern a large swath of subsidence in the deep tropics stretching across the Pacific Ocean the past 6 weeks has suppressed tropical activity (Fig. 1). The 2-week forecast indicates not much change…the MJO is persistent in the west/central Indian Ocean equatorial region (Fig. 2). Residual influences has been a generally wet climate near or across parts of India arcing northeastward into China. Farther downstream the Australian climate has been dry in this (MJO) pattern.

Interestingly, the stalled MJO in the far western Indian Ocean is very supportive of strong tropical waves moving into the eastern tropical North Atlantic. However, early-to-middle July is still early for tropical cyclones to emerge in the outer tropical North Atlantic. The Sahara dust cloud pattern across the tropical North Atlantic is also suppressing early season activity in the North Atlantic deep tropics. The MJO location in eastern tropical Africa/western Indian Ocean tropics has contributed to a light shear upper environment across the tropical North Atlantic. Once the Saharan dust cloud regime eases the North Atlantic tropics should see an uptick in tropical cyclone activity.