Global Tropics Hazards and Benefits Outlook Discussion (from NOAA)
Last Updated: 04.04.17 Valid: 04.05.17 - 04.18.17
The MJO remained weak during the past week based on diagnostic tools including the CPC velocity potential-based index and the RMM index. The low frequency state, with enhanced convection across the Maritime Continent and far eastern Pacific, continues to be a major influence on anomalous convection throughout the global tropics. Dynamical model forecasts of the RMM index maintain a weak MJO signal during the next week, though there are some models indicating a signal over the West Pacific. The signal over the West Pacific is likely related to predicted tropical cyclone activity in the South Pacific and near Australia. Additionally, some observational tools indicate the presence of a robust equatorial Rossby Wave over the Maritime Continent. Therefore, the MJO contribution to anomalous convection across the global tropics and effects on the extratropical circulation are expected to be minimal.
No new tropical cyclones developed during the past week. During the next 2 weeks, tropical cyclone formation odds are likely to be enhanced northwest of Australia, over the Coral Sea, and over the South Pacific. The signal in the South Pacific is especially high during the earliest portions of the outlook period. The signal over the South Pacific, shifts slightly west during the 2 week period, with the Coral Sea. Northwest of Australia, the signal peaks late in Week-1, with lowered confidence for a Week-2 formation, but the threat straddles the break in the period.
The favored areas of anomalous rainfall across the global tropics during the next two weeks are based on consensus among the CFS, GFS, and ECMWF models along with the low frequency state and the potential impacts of the equatorial Rossby Wave, currently over the Maritime Continent. During Week-1, enhanced (suppressed) convection is likely over the Maritime Continent (central Pacific) where the low-frequency state and the equatorial Rossby Wave are likely to constructively interfere. The wet signal over the Maritime Continent is forecast to spread westward through Week-2, while the dry signal in the central Pacific is likely to be reduced in coverage from Week-1, but still present, as it is related to the low-frequency signal. Heavy rains are likely over the eastern Pacific and northwest South America, related to the low-frequency pattern.
Forecasts over Africa are made in consultation with CPCs international desk, and can represent local-scale conditions in addition to global-scale variability.