Asia & South America Seasonal Outooks
By
Jason Nicholls, AccuWeather senior meteorologist &
Lead International Forecaster
Updated Aug 31, 2021 11:42 AM EDT
As boreal summer and austral winter wind down, we will take a look ahead to boreal autumn for Asia and austral spring for South America. Before getting into the outlooks, we will briefly cover some current teleconnection and analog years used.
Looking at the latest sea-surface temperature anomalies across the globe we see three SST-based teleconnections that should be a factor heading into the SON period. There is currently a negative Indian Ocean Dipole (IOD) and the -IOD will likely persist through much of boreal autumn/austral spring. Atlantic Nino conditions remain in place, resulting in plenty of warm water off northern Brazil. The Atlantic Nino is expected to gradually weaken over the next few months but should persist into October.
The other area to watch is the equatorial Pacific where there is currently a weak central Pacific La Nina look to water temperatures. Most modeling and teleconnections favor La Nina conditions returning over the next few months. Initially the sea-surface temperatures may favor central Pacific La Nina or La Nina Modoki-like conditions before becoming a more traditional eastern Pacific based La Nina by the end of 2021.
Below is a composite for rainfall and temperature anomalies around the globe for September, October and November during La Nina Modoki years.
Taking into account all teleconnections, we came up with a few analog years we like which resulted in the following upper air pattern, precipitation anomalies and temperature anomalies.
There are some similarities between the analogs and modeling (shown below). Notably the favoring of above-normal rainfall around the Philippines and southeast Asia, while the models are drier in the Middle East than the analogs. In South America, there is a notable difference with the analogs favoring drier weather in northern Brazil while most modeling showing these areas as wetter than normal. Southern Brazil is also shown to be drier on most modeling than the analogs show.
It would be nice to have analogs and modeling in agreement, but it does not always work out that way. To come up with the seasonal outlooks we tried to lean toward what we think will be the main teleconnections. First taking a look at Asia for boreal autumn.
We believe the -IOD and weak La Nina Modoki conditions will lead to wetter-than-normal conditions across southeast Asia into the Philippines. Southern India, in turn, should be drier than normal with what looks to be lackluster northeast monsoon season. We will need to watch the Southern Oscillation Index over the next couple of months for timing the onset of the northeast monsoon. At this point, the northeast monsoon is expected to reach Tamil Nadu a little later than the normal mid-October onset.
A jet displaced a little farther north than usual should result in much of the Middle East being drier and warmer than normal during autumn. The exception will be the southern Arabian Peninsula where we expect near- to above-normal rainfall mostly owing to good rainfall early in the season before turning typically drier late in the season. Eastern Asia will also be a tale of two seasons with a good chance for above normal rainfall from northeast China across the Korean Peninsula to Japan early in the season. These areas can trend drier late in the season. Southeast China will have near- to above-normal rainfall overall, though the second half of the season may be wetter than the start.
Much of Asia should have near- to above-normal temperatures while the tropics will remain the wildcard. In the west Pacific we expect the basin to turn more active later in September and that will possibly continue into October. The basin may turn less active in November. The favored areas for development and impacts will be from around the Philippines to southeast Asia and perhaps southeast China. However, one or two impacts are possible in the Korean Peninsula and Japan early in the season.
We are expecting two to four tropical systems to form in the northern Indian Ocean during October and November with the better chance for development expected to be over the Bay of Bengal. Of these two to four systems, we are expected one to two to become a cyclonic storm or strong with the Bay of Bengal also being favored for such activity. If a depression or cyclone were to impact southern India during the October and November time frame, then southern Andhra Pradesh, Tamil Nadu, Kerala and Karnataka could end up being wetter than forecast.
Shifting gears to South America, here is our outlook for their spring. The two main factors in this area should be the developing La Nina as well as the warm waters off northern Brazil. Cooler-than-normal waters are expected to persist off the coast of southeast Brazil as well as northern and central Chile, which should have some impact on the weather in these areas.
Overall we expect northern Brazil to Venezuela and Colombia to turn wetter than normal which can result in temperatures near to slightly below normal in these areas. Southern Brazil, Uruguay and northern Argentina will likely start the season with near- to above-normal rainfall but should turn drier during October and November. Temperatures will likely average warmer than normal for the season, but temperatures may be closer to seasonable levels early in the season.
The cool waters off central and northern Chile should keep much of Chile drier than normal with temperatures near to slightly warmer than normal. However, there is a chance for a couple of light rain events into central Chile, especially early in the season. Meanwhile, southern Chile will continue to experience storms during September and perhaps into October before turning drier later in the season. The early storminess can result in precipitation averaging near to above normal for the season and may hold temperatures closer to normal in southern Chile.
The expected development of La Nina should result in rainfall being below normal across much of Ecuador into Peru with temperatures near to slightly above normal in these areas.
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Weather Blogs / Global weather
Asia & South America Seasonal Outooks
By Jason Nicholls, AccuWeather senior meteorologist & Lead International Forecaster
Updated Aug 31, 2021 11:42 AM EDT
As boreal summer and austral winter wind down, we will take a look ahead to boreal autumn for Asia and austral spring for South America. Before getting into the outlooks, we will briefly cover some current teleconnection and analog years used.
Looking at the latest sea-surface temperature anomalies across the globe we see three SST-based teleconnections that should be a factor heading into the SON period. There is currently a negative Indian Ocean Dipole (IOD) and the -IOD will likely persist through much of boreal autumn/austral spring. Atlantic Nino conditions remain in place, resulting in plenty of warm water off northern Brazil. The Atlantic Nino is expected to gradually weaken over the next few months but should persist into October.
The other area to watch is the equatorial Pacific where there is currently a weak central Pacific La Nina look to water temperatures. Most modeling and teleconnections favor La Nina conditions returning over the next few months. Initially the sea-surface temperatures may favor central Pacific La Nina or La Nina Modoki-like conditions before becoming a more traditional eastern Pacific based La Nina by the end of 2021.
Below is a composite for rainfall and temperature anomalies around the globe for September, October and November during La Nina Modoki years.
Taking into account all teleconnections, we came up with a few analog years we like which resulted in the following upper air pattern, precipitation anomalies and temperature anomalies.
There are some similarities between the analogs and modeling (shown below). Notably the favoring of above-normal rainfall around the Philippines and southeast Asia, while the models are drier in the Middle East than the analogs. In South America, there is a notable difference with the analogs favoring drier weather in northern Brazil while most modeling showing these areas as wetter than normal. Southern Brazil is also shown to be drier on most modeling than the analogs show.
It would be nice to have analogs and modeling in agreement, but it does not always work out that way. To come up with the seasonal outlooks we tried to lean toward what we think will be the main teleconnections. First taking a look at Asia for boreal autumn.
We believe the -IOD and weak La Nina Modoki conditions will lead to wetter-than-normal conditions across southeast Asia into the Philippines. Southern India, in turn, should be drier than normal with what looks to be lackluster northeast monsoon season. We will need to watch the Southern Oscillation Index over the next couple of months for timing the onset of the northeast monsoon. At this point, the northeast monsoon is expected to reach Tamil Nadu a little later than the normal mid-October onset.
A jet displaced a little farther north than usual should result in much of the Middle East being drier and warmer than normal during autumn. The exception will be the southern Arabian Peninsula where we expect near- to above-normal rainfall mostly owing to good rainfall early in the season before turning typically drier late in the season. Eastern Asia will also be a tale of two seasons with a good chance for above normal rainfall from northeast China across the Korean Peninsula to Japan early in the season. These areas can trend drier late in the season. Southeast China will have near- to above-normal rainfall overall, though the second half of the season may be wetter than the start.
Much of Asia should have near- to above-normal temperatures while the tropics will remain the wildcard. In the west Pacific we expect the basin to turn more active later in September and that will possibly continue into October. The basin may turn less active in November. The favored areas for development and impacts will be from around the Philippines to southeast Asia and perhaps southeast China. However, one or two impacts are possible in the Korean Peninsula and Japan early in the season.
We are expecting two to four tropical systems to form in the northern Indian Ocean during October and November with the better chance for development expected to be over the Bay of Bengal. Of these two to four systems, we are expected one to two to become a cyclonic storm or strong with the Bay of Bengal also being favored for such activity. If a depression or cyclone were to impact southern India during the October and November time frame, then southern Andhra Pradesh, Tamil Nadu, Kerala and Karnataka could end up being wetter than forecast.
Shifting gears to South America, here is our outlook for their spring. The two main factors in this area should be the developing La Nina as well as the warm waters off northern Brazil. Cooler-than-normal waters are expected to persist off the coast of southeast Brazil as well as northern and central Chile, which should have some impact on the weather in these areas.
Overall we expect northern Brazil to Venezuela and Colombia to turn wetter than normal which can result in temperatures near to slightly below normal in these areas. Southern Brazil, Uruguay and northern Argentina will likely start the season with near- to above-normal rainfall but should turn drier during October and November. Temperatures will likely average warmer than normal for the season, but temperatures may be closer to seasonable levels early in the season.
The cool waters off central and northern Chile should keep much of Chile drier than normal with temperatures near to slightly warmer than normal. However, there is a chance for a couple of light rain events into central Chile, especially early in the season. Meanwhile, southern Chile will continue to experience storms during September and perhaps into October before turning drier later in the season. The early storminess can result in precipitation averaging near to above normal for the season and may hold temperatures closer to normal in southern Chile.
The expected development of La Nina should result in rainfall being below normal across much of Ecuador into Peru with temperatures near to slightly above normal in these areas.
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