During which stage do surface pressure values approach 1000 hPa in tropical cyclones?

In tropical cyclones, surface pressure values approaching 1000 hPa are typically observed during the formative stage. This stage marks the initial development of the cyclone, where it begins to organize and intensify. At this point, warm, moist air is being drawn into the developing system, leading to a decrease in surface pressures as the storm starts to strengthen.

During the formative stage, the cyclone is not yet fully developed, and the pressures are higher compared to the later stages of the cyclone's life cycle. As the storm continues to strengthen through the immature and mature stages, the central surface pressure may drop significantly below 1000 hPa, which is indicative of a well-organized and strong tropical cyclone. Thus, the formative stage is characterized by surface pressures that are beginning to lower but are still near the 1000 hPa mark.