When will the tropical Western Pacific become active?
By
Jason Nicholls, AccuWeather senior meteorologist
Published Jul 9, 2020 3:38 PM EST
The 2020 Western Pacific typhoon season has produced two named storms thus far. The first storm was Typhoon Vongfong which developed on 10 May then dissipated on 18 May after impacting the northern Philippines. The most recent storm was Tropical Storm Nuri which formed on 10 June and dissipated on 14 June. The basin has been quiet since Nuri which means there have been no named storms in the western Pacific for about three weeks. In contrast, there were four named storms in the western Pacific by this point in 2019.
The peak period for tropical cyclone activity in the western Pacific usually runs from May through October, so the question is when can we expect the basin to spring back to life? Looking at the recent satellite image, we can see that the basin remains void of organized tropical features.
The main reason behind the quiet spell across the western Pacific is likely tied to the Madden-Julian Oscillation, or MJO, being stalled in phases 1, 2 and 3 since late May. These phases tend to favor tropical activity in the eastern Pacific and Atlantic which we have seen during June. The most favorable phases for western Pacific tropical development tends to occur in phases 6 and 7.
The MJO forecasts, above, show no signs of the MJO reaching the favorable phases of 6 and 7 anytime soon, but that does not necessarily mean a tropical cyclone cannot develop in the other phases. The chances are just not as high in phases 2 and 3.
The operational global models do not show any development in the basin over the next two weeks, but we are watching for a small window of development late in week 2 into week 3 of July. Looking at the CFS forecast for outgoing long wave radiation, we can see an equatorial Rossby wave and Kelvin wave are expected to cross the basin between the date line and the Mariana Islands in this period.
These atmospheric waves coupled with favorable 200 mb vertical velocities can help spin up a tropical low or depression from around the Mariana Islands to around the Marshall Islands sometime late next week into early the following week. However, the chance of a named tropical storm still looks low for now but is not out of the realm of possibility given the warm waters in the region and shear expected to be light to moderate.
The cross-section look at the region around the Mariana Islands and the Marshall Islands also shows an equatorial Rossby wave in the vicinity of the Mariana or the Marshall Islands around 21 or 22 July.
It appears that if a tropical feature were to develop late next week into early the following week its main impact would be heavy rain across the Mariana Islands, but it may otherwise have minimal land impacts.
Looking at the preceding charts, it appears that if a tropical cyclone fails to develop in the small window between 16 and 23 July, there may not be a named feature in the western Pacific until late July or early August at the earliest. Continue to check back at AccuWeather.com for updates on the basin.
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Weather Blogs / Global weather
When will the tropical Western Pacific become active?
By Jason Nicholls, AccuWeather senior meteorologist
Published Jul 9, 2020 3:38 PM EST
The 2020 Western Pacific typhoon season has produced two named storms thus far. The first storm was Typhoon Vongfong which developed on 10 May then dissipated on 18 May after impacting the northern Philippines. The most recent storm was Tropical Storm Nuri which formed on 10 June and dissipated on 14 June. The basin has been quiet since Nuri which means there have been no named storms in the western Pacific for about three weeks. In contrast, there were four named storms in the western Pacific by this point in 2019.
The peak period for tropical cyclone activity in the western Pacific usually runs from May through October, so the question is when can we expect the basin to spring back to life? Looking at the recent satellite image, we can see that the basin remains void of organized tropical features.
The main reason behind the quiet spell across the western Pacific is likely tied to the Madden-Julian Oscillation, or MJO, being stalled in phases 1, 2 and 3 since late May. These phases tend to favor tropical activity in the eastern Pacific and Atlantic which we have seen during June. The most favorable phases for western Pacific tropical development tends to occur in phases 6 and 7.
The MJO forecasts, above, show no signs of the MJO reaching the favorable phases of 6 and 7 anytime soon, but that does not necessarily mean a tropical cyclone cannot develop in the other phases. The chances are just not as high in phases 2 and 3.
The operational global models do not show any development in the basin over the next two weeks, but we are watching for a small window of development late in week 2 into week 3 of July. Looking at the CFS forecast for outgoing long wave radiation, we can see an equatorial Rossby wave and Kelvin wave are expected to cross the basin between the date line and the Mariana Islands in this period.
These atmospheric waves coupled with favorable 200 mb vertical velocities can help spin up a tropical low or depression from around the Mariana Islands to around the Marshall Islands sometime late next week into early the following week. However, the chance of a named tropical storm still looks low for now but is not out of the realm of possibility given the warm waters in the region and shear expected to be light to moderate.
The cross-section look at the region around the Mariana Islands and the Marshall Islands also shows an equatorial Rossby wave in the vicinity of the Mariana or the Marshall Islands around 21 or 22 July.
It appears that if a tropical feature were to develop late next week into early the following week its main impact would be heavy rain across the Mariana Islands, but it may otherwise have minimal land impacts.
Looking at the preceding charts, it appears that if a tropical cyclone fails to develop in the small window between 16 and 23 July, there may not be a named feature in the western Pacific until late July or early August at the earliest. Continue to check back at AccuWeather.com for updates on the basin.
Report a Typo