A New Challenger Approaches – The MJO and Typhoon Lan

Valid October 19, 2017 at 9:00 AM CT

Note: The tropical blog is back rolling again, this week with a focus on the Madden-Julian Oscillation and its impacts on the development of tropical cyclones. Specifically, the focus of TC development will be on Typhoon Lan, a very strong storm heading towards Japan.

Little do many casual observers of tropical weather know that there is more to this area of the world than tropical storms, hurricanes, and typhoons. Waves, oscillations, and cycles within the atmosphere play a key role in the development, formation, and strengthening of tropical cyclones. The focus now turns to one of these players, the Madden-Julian Oscillation, and its current role in the western Pacific.

Welcome to the MJO

The Madden-Julian Oscillation (MJO) is a broad-scale perturbation in the atmosphere (and ocean to an extent) that typically lasts for 30 to 60 days. This oscillation propagates eastward, generally through eight phases, representing the different parts of the world it is traversing. The most efficient way to track this is through Real-Time Multivariate MJO (RMM) diagrams.


Figure 1 – The latest RMM diagram for the MJO from the Australian Bureau of Meteorology.

The latest RMM diagram from the Australian Bureau of Meteorology shows the latest propagation of the oscillation into the maritime continent, known more commonly as southeast Asia. The area within the circle is the time over which the MJO is considered weak, comprised of most of September and into early October. The MJO can be expected to continue to propagate eastward into the western Pacific Ocean, while continuing to remain strong as it is now.

Impacts from the MJO can be expected to expand beyond its current location. Changing phases of the MJO have been linked to changes in tropical cyclone development, triggering of changes in ENSO cycles, the timing and strength of monsoon conditions in Asia and Australia, and changes in the jet stream location over the Northern Hemisphere mid-latitudes in winter. However, the primary focus currently sits on the development of Typhoon Lan in the western Pacific basin.

Japan’s Newest Monster


Figure 2 – The projected path of Typhoon Lan, with Japan directly in its crosshairs.

Typhoon Lan currently has maximum winds near its center of 100 knots, or 115 miles per hour, per the Japanese Meteorological Agency (JMA). For comparison, that would be classified as a major hurricane in the Atlantic basin. Forecasts from both the JMA and the Joint Typhoon Warning Center (JTWC) expect further strengthening from Lan, with the JTWC expecting it to become a Super Typhoon before its impacts are felt in Japan.

How does the development of Lan connect to the MJO, however? This oscillation is usually identified by anomalous increases in convection, specifically over the Indian Ocean. However, this convection generally propagates with the oscillation, though these convectively-coupled waves move slower with stronger convection. Typhoon Lan could represent this strong area of convection, coupled with a few other strong atmospheric ingredients.



Figure 3 – Lower level convergence (top) and upper level divergence (bottom) over the western Pacific Ocean.

Anomalously high lower level convergence and upper level divergence is observed not only over Typhoon Lan, but over most of the Philippines and parts of Indonesia. This is a positive sign for the strength of the typhoon and its ability to in part “make its own environment”, but also speaks to the benefits of the MJO for this storm. While the deep layer wind shear does not appear favorable ahead of Lan, the storm may continue to push more favorable shear conditions out ahead of it, with shear tendency generally neutral along its path.


Figure 4 – Total Precipitable Water (TPW) over the western Pacific Ocean, with Typhoon Lan as the large pink feature.

The total precipitable water (TPW) feature for Typhoon Lan is impressive, and shows the stream of moisture from the general location of the MJO. The flow of TPW from southern Vietnam, across Indonesia, and into Lan shows there is plenty of available moisture for this storm.

Typhoon Lan is expected to continue to strengthen and push northward toward Japan, before recurving just off the Japanese coastline. Unlike many Atlantic basin storms, Lan has much of its convection concentrated on the southern end of the system, but may redistribute depending on further strengthening and development.

Other Tropical Tidbits

All is quiet on the eastern front, with the Atlantic basin not expecting tropical cyclone activity for the next 48 hours. The eastern and central Pacific remain silent as well. Meanwhile, in hurricane-ravaged Puerto Rico, recovery remains at a snail’s pace one month after Maria hit. The Governor of the island will meet with the President today to negotiate for further aid. Finally, Mississippi State University’s men’s basketball team will host Nebraska in an exhibition game on Sunday, with proceeds going to hurricane relief efforts in Florida.

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