On August 9, a tropical wave entered the Atlantic and moved quickly westward. From the start, the system produced an impressive area of thunderstorms, but its quick motion slowed down development. Four days later, it became organized enough to be designated Tropical Depression Seven well east of the Lesser Antilles. The storm covered ground rapidly, and was approaching the Windward Islands by the next day when it was upgraded to Tropical Storm Grace. Despite the upgrade, aircraft reconaissance indicated that the cyclone had serious structural issues: the low-level center was very ill-defined and difficult to even identify. In fact, sometime around August 14, Grace might have opened up into a trough of low pressure.
Nevertheless, the system was maintained as a tropical cyclone through the 14th, though it did weaken to a depression south of Puerto Rico. Disorganized thunderstorms extended from north of Puerto Rico to well south of the Dominican Republic by the next day along the former tropical wave axis. There were several areas of vorticity, but Grace consolidated some toward the southern end that evening. On August 16, the center was better defined and Grace clipped the souternmost point of the Dominican Republic, still as a tropical depression. Heavy rainfall in Hispaniola led to the risk of mudslides and flooding.
Land interaction lessened from that point and Grace slowly became a bit better organized as the strong subtropical ridge continued to push it just north of west. The center passed just south of Haiti that night, thankfully sparing the country the heaviest rainfall. Early on August 17, the storm regained tropical storm strength just in time for a direct hit on the island of Jamaica. The small country was not enough to significantly disrupt the cyclone, and in fact it strengthened gradually and grew in size that day. By the time it emerged off the west coast of Jamaica, Grace was a strong tropical storm.
Now over open water, the storm could tap into the highest oceanic heat content anywhere in the Atlantic. Relative humidity levels near Grace were only moderate (in the 50-60% range), which slowed the storm's intensification with occasional dry air intrusions. Otherwise, there was little to stop its strengthening and the cyclone was upgraded to a hurricane on August 18. The storm reached its first peak intensity of 80 mph winds and a pressure of 986 mb overnight before making landfall in the northern Yucatan peninsula before sunrise on August 19. The storm weakened over land and became a tropical storm late that morning, but maintained a vigorous circulation and emerged as a still strong tropical storm into the Bay of Campeche that evening.
Atmospheric conditions were better in the southern Gulf of Mexico than they had been over the Caribbean, with ample moisture in the air. It didn't take long for Grace to take advantage. By the morning of August 20, it had regained hurricane strength and extremely deep convection began firing north and east of the center. This managed to wrap all the way around by the afternoon and the cyclone rapidly intensified. Remarkably, it went from a category 1 to a high-end category 3 by late that night, becoming the first major hurricane of the 2021 season. An eye feature began to clear out just before Grace made its final landfall in Mexico very early in the morning on August 21. At landfall, Grace had an estimated peak intensity of 125 mph sustained winds and a minimum central pressure of 962 mb. This was the highest windspeed in a recorded landfall along the Mexican Gulf coast south of Tampico, surpassing Karl of 2010.
After moving inland, the mountainous terrain of Mexico quickly weakened the cyclone, bringing it to a tropical storm by that afternoon. Grace dissipated entirely by that evening after bringing heavy precipitation even as far as Mexico City. The remnants continued into the eastern Pacific ocean and ultimately reformed into a tropical storm early on August 23. Since the circulation had dissipated and reformed, however, the cyclone received a new name: Tropical Storm Marty. Marty persisted for only a few days before becoming post-tropical.
The above image is an infrared satellite view of Grace on the night of its final landfall in Mexico as a major hurricane.
A strong subtropical ridge kept Grace moving on a steady trajectory just north of west for almost its entire existence.
No comments:
Post a Comment