Modifying the ARCHER algorithm to improve the tracking of weak tropical cyclones in the western North Pacific

Accurate identification of the center of a tropical cyclone (TC) is crucial for TC forecasting and early warning. For weak TCs [i.e., maximum sustained wind (MSW) ≤17 m/s], the determination of their near-surface centers is more challenging due to weaker central convection and less pronounced circulation features. Existing objective TC positioning methods often exhibit limited performance for weak TCs, and few are specifically designed for weak TCs. The Automated Rotational Center Hurricane Eye Retrieval (ARCHER) algorithm, which locates TC centers by jointly finding the spiral cloud band center and assumed eye center in satellite images, is a relatively accurate and objective approach. However, it was designed primarily for use with TCs of at least tropical storm intensity (MSW ⩾17.2 m/s) and it is less effective for weaker TCs. This study analyzed 8000 TC samples in the western North Pacific (WNP) during 2000–2012 to develop M_ARCHER, a modified version of the ARCHER algorithm with adjusted parameters to locate the centers of weak TCs in the WNP. M_ARCHER employs two sets of new optimized parameters tailored for microwave and infrared satellite observations. These parameters include the inclination angle of the spiral cloud band pattern, range and increment for determining the assumed eyewall inner edge radius, and the weights assigned to spiral and eye centering, among others. These modifications improve the algorithm’s capability to detect the asymmetric and less-defined structures of weak TCs. Independent tests of the M_ARCHER algorithm show median location errors for weak TCs of 44 km (microwave) and 57 km (infrared) relative to the China Meteorological Administration best track data. For readily available infrared observations, M_ARCHER shows a 20% improvement in location accuracy relative to the original algorithm. Notably, strong wind shear can disrupt the structure of a TC, making the spiral-eye configuration within the M_ARCHER unrealistic and reducing the location accuracy.