Jet streams are relatively narrow bands of strong west-to-east winds in the upper troposphere. In the zonal-mean climatology, there are two jet streams, the subtropical jet (STJ) and polar front jet (PFJ), located in both the Northern Hemisphere (NH) and Southern Hemisphere (SH). The STJ is commonly viewed as being driven by the angular momentum conservation in the poleward flowing upper tropospheric branch of the tropical Hadley circulation (Held & Hou, 1980;Schneider, 1977), and thus it is located near the poleward edge of Hadley Cell in each hemisphere. The PFJ is driven by the convergence of momentum by transient midlatitude eddies (Held, 1975;Panetta, 1993) and is consequently located at midlatitudes where baroclinic instability is strongest.

Although the multi‐model average compares well with observations, individually most of the latest climate models do not simulate a realistic size of the Indo‐Pacific Warm Pool in the present‐day climate. This study explores the implications of this warm pool size bias in climate models in Northern Hemisphere winter. The warm pool size bias in phase 6 of the Coupled Model Intercomparison Project models is related to the subtropical jet and precipitation distribution, both in the present‐day climate and in response to climate change, through extratropical Rossby wave trains and tropical circulation pathways. Based on these relationships, emergent constraints are developed to observationally constrain the future subtropical jet response over Asia and the Atlantic Ocean and precipitation response over North and Central America, which can help to reduce uncertainty in future projections of these features. Thus, accurate model simulation of the warm pool in the present‐day climate is important for future projections of the subtropical jet and precipitation.

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