Heavy Rains Indicated Southeast Brazil Days 8-14

November Optimum Climate Normal
09/29/2021, 2:11 pm EDT
U.S. Temperature/Precipitation Rankings for Mid-to-Late Summer 2021
10/11/2021, 5:02 am EDT
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A wet fetch out of the deep tropics interacts with a low pressure trough causing excessive rainfall forecast by GFS in the 8-14-day period across Southeast Brazil, Uruguay and northeast Argentina.

CIC AG Sunday Report Highlights: Great Plains, Brazil and South-central Europe big rains!

Fig. 1-2: The GFS day 6-10/day 11-15 rainfall forecast across the U.S. AG Belt.

Great Plains discussion: This week is dry and warm across the Great Plains. However, an upper trough moves into the West Coast later this week and amplifies. In-between the cooling weather pattern in the West, and the lingering very warm pattern in the Central and East U.S. an area of showers with thunderstorms develops in the 6-10-day forecast across the Great Plains according to the 12Z GFS (Fig. 1). Some of the rain could be heavy with more than one event. Temperatures start to cool mid-to-late days 6-10. In the 11-15-day period the East U.S. resists any cooling while the western chill moderates but manages to shift into the Great Plains. Once again, the cold front separating the two thermal regimes stagnates and focuses potentially excessive rainfall in the Mid-south U.S. and northeast Great Plains (Fig. 2). Also, note the persistent heavy rain off the South Carolina Coast. This feature is a slow-moving tropical system. North of the tropical event the high-pressure ridge stays intact to keep the rain-triggering cold front in the Central U.S. quasi-stationary.

South America discussion: The forecast trends much wetter over-the-weekend. Today’s 12Z GFS is the wettest model but indicates the potential amount ahead most-focused on the medium-range. In the 7-day forecast, a stalled cold front will trigger up to 4 in. of rain across Interior Southeast Brazil (Fig. 3). The largest forecast change is in the 8-14-day period. A wet fetch out of the deep tropics is invited south into a frontal trough triggering widespread heavy rains (Fig. 4).

Fig. 3-4: The GFS day 1-7/day 8-14 rainfall amount forecast for South America.

Australia and Europe discussion: A broad wetter than normal regime is forecast across the eastern half of Australia the next 15 days (Fig. 5). Excessive amount is not indicated. The 15-day rainfall anomaly forecast for Europe indicates two zones of excessive precipitation. A cutoff upper low-pressure system is a slow-mover and causes heavy rains across South-central Europe the next 2 weeks (Fig. 4). West-coastal Scandinavia is in a wet fetch of heavy rainfall the next 2 weeks.

Fig. 5-6: The ECM ENS 15-day percent of normal rainfall forecast across Australia and the Europe rainfall anomaly forecast for the next 15 days.