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<p>We have analyzed the modulation of TC formations in the western North Pacific (WNP) during July-October by El NinÌ o (EN), La NinÌ a (LN), and the Madden Julian Oscillation (MJO). This analysis was conducted from the perspective of several large scale environmental factors (LSEFs) that strongly influence tropical cyclone (TC) formation: sea surface temperature (SST), low level relative vorticity, vertical wind shear, and upper level divergence. We examined the variations in each LSEF associated with EN, LN, and MJO. We used composite LSEFs for EN, LN, and each of the eight MJO phases to force the Naval Postgraduate School (NPS) statistical model for calculating TC formation probabilities. We then compared the resulting probabilities to actual formations to determine how accurately the model represented ENLN and MJO related variations in TC formations. The model based probabilities provide a realistic quantitative representation of how ENLN and MJO make TC formation more and less likely in the WNP. Our results should be useful in improving the education, training, and environmental situational awareness of TC forecasters. Our results also indicate that the NPS model has the potential to improve operational forecasting of TC formations in the WNP, if forced by skillful forecasts of the LSEFs.
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<br>Subjects: Meteorology; Oceanography; Cyclones; Tropics; Forecasting</div>
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Johnson, Stephanie A.</div>
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