This study investigates the water vapor transport to the Tibetan Plateau (TP) induced by Bay of Bengal (BOB) tropical cyclones (TCs) in May during 1979-2019. The water vapor around the BOB TCs can be transported to the south of the TP by the southerlies at the upper troposphere east of the TC center. Whether the water vapor can cross the southern boundary of the Tibetan Plateau (SBTP) may rely on the different configurations of BOB TCs and long-wave trough and ridge. We found that the water vapor may (may not) cross SBTP if the TC’s wind field converges with the westerlies in front of the trough (ridge).
  The physical mechanism is explored according to the momentum equation. When the TC moves northward around the SBTP, its wind field could interact with the trough (Type-T TC) and ridge (Type-R TC) in the westerlies. In the area close to the trough line (ridge line), the meridional acceleration is positive (negative), hence meridional component of velocity increases (decreases). Therefore, it is more favorable for the water vapor transported northward if a Type-T TC enters the westerlies from the area close to the trough line than the ridge line. The simulation of the BOB TC cases configuration using WRF model confirms the importance of the relative position between the Type-T TC and the SBTP to the water vapor transport over the SBTP. For the Type-T TC, the meridional moisture budget over the SBTP is positively correlated with the TC intensity and negatively correlated with the distance between the TC center and the SBTP. However, for the Type-R TC, the meridional moisture budget is not related to the TC intensity and the distance. The configuration of TC and long-wave trough or ridge may be predictable through the intraseasonal oscillation activity in the eastern BOB and the southern Arabian Sea.

孟加拉湾；热带气旋；水汽输送；,动量方程