<P> Following its designation, the tropical storm moved swiftly westward into the Caribbean Sea, under the influence of an expansive ridge of high pressure to its north . An environment of moderate wind shear complicated the weather of the storm's intensity, with global forecast models suggesting dissipation in the central Caribbean, whereas statistical and hurricane models suggested the potential for Harvey to come near hurricane strength in later days . Over the next day, the storm changed little in structure, remaining poorly organized with its low - level center on the eastern edge of associated deep convection . Harvey's presentation began to deteriorate early on August 19; its convective pattern became elongated while the circulation became less defined . In fact, a reconnaissance aircraft was unable to find a loosely - closed circulation at 850 mb (4,781 ft), though it did locate one at lower levels . Harvey was downgraded to a tropical depression at 21: 00 UTC on August 19; six hours later, based on continued data from a reconnaissance aircraft, it was declared an open tropical wave . </P> <P> Early on August 20, the NHC began monitoring the remnants of Harvey for redevelopment . Although the effects of strong upper - level winds and dry air were expected to limit development in the near - term, conditions were expected to become more conducive to tropical storm and hurricane conditions when the disturbance entered the northwestern Caribbean Sea, and especially in the Bay of Campeche . Despite an increase in convective organization, the disturbance still lacked a well - defined center as it approached the Yucatán Peninsula . While traversing inland, satellite images and surface observations indicated that the circulation became better defined . </P> <P> A reconnaissance aircraft investigating the remnants of Harvey around 15: 00 UTC on August 23 indicated that it once again acquired a well - defined center, and the NHC upgraded it to a tropical depression accordingly . The system began to slowly consolidate amid an increasingly favorable environment, attaining tropical storm intensity by 06: 00 UTC on August 24 . Later that morning, Harvey began to undergo rapid intensification as an eye developed and its central pressure quickly fell . By 17: 00 UTC, the storm was upgraded to the third hurricane of the season . Slight entrainment of dry air slowed the intensification process, however, by the next day, Harvey was able to quickly strengthen into a Category 3 major hurricane by 19: 00 UTC . Further deepening occurred as the storm approached the coast of Texas, with Harvey becoming a Category 4 hurricane at 23: 00 UTC, based on reconnaissance aircraft data . Around 03: 00 UTC on August 26, the hurricane made landfall at peak intensity at Rockport with winds of 130 mph (215 km / h) and an atmospheric pressure of 938 mbar (27.7 inHg). Harvey became the first major hurricane to make landfall in the United States since Wilma in 2005 and the strongest in terms of wind speed to hit the country since Charley in 2004 . It was the first hurricane to strike Texas since Hurricane Ike in 2008, the first major hurricane in the state since Bret in 1999, and the strongest in Texas since Carla in 1961 . </P> <P> After striking land, the storm moved over the Copano Bay and made a second landfall in Texas just north of Holiday Beach at 06: 00 UTC on August 26 as a Category 3 hurricane . Afterwards, rapid weakening ensued as its speed slowed dramatically to a crawl, and Harvey weakened to a tropical storm at 18: 00 UTC on August 26 . For about two days the storm stalled just inland, dropping very heavy rainfall and causing widespread flash flooding . Harvey's center drifted back towards the southeast, positioning itself near or just off the Texas coast at Matagorda by 15: 00 UTC on August 28 . Once offshore, convection blossomed and allowed the once - exposed low - level circulation to become obscured . An Air Force reconnaissance plane investigating the system during the afternoon of August 29 found that maximum winds had increased to 50 mph (85 km / h). Around 09: 00 UTC the next morning, Harvey made its third and final landfall just west of Cameron, Louisiana, with winds of 45 mph (75 km / h). </P>

When did hurricane harvey become a category 4
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