<P> A central dense overcast and favorable outflow developed atop the center of circulation, which enabled Maria to become further organized throughout the early morning hours of September 17 . After a brief intrusion of dry air exposed the circulation, a convective burst occurred over the center and intensification resumed . Hurricane Hunters investigating the system observed surface winds of 74 mph (119 km / h) and a formative eye feature . Accordingly, the NHC upgraded Maria to hurricane status at 21: 00 UTC . Expansion of the central dense overcast and an increasingly complete eyewall signaled steady intensification throughout the overnight of September 17--18 . Considerable lightning activity was identified within the hurricane's core early on September 18 and statistical models indicated a high probability of rapid intensification . Explosive strengthening took place shortly thereafter, with aircraft reconnaissance finding surface winds of 120 mph (195 km / h) and a central pressure of 959 mbar (hPa; 28.32 inHg), making Maria a Category 3 hurricane on the Saffir--Simpson scale, and hence a major hurricane . Additionally, radar data revealed a well - defined 12 mi (19 km) wide eye . The eye contracted slightly to 9 mi (14 km) as intensification continued, and the system reached Category 4 strength by 21: 00 UTC . </P> <P> Rapid intensification culminated late on September 18, with Maria achieving Category 5 status just 15 mi (25 km) east - southeast of Dominica . Hurricane Hunters observed surface winds of 160 mph (260 km / h) and a pressure of 925 mbar (hPa; 27.32 inHg) at this time . Maria made landfall in Dominica at 01: 15 UTC on September 19, becoming the first Category 5 hurricane on record to strike the island nation . Interaction with the mountains of Dominica imparted slight weakening of the hurricane to Category 4; however, once over the Caribbean Sea Maria regained Category 5 intensity . Additional strengthening took place as the storm tracked northwest toward Puerto Rico . Despite the formation of concentric eyewalls--the larger one spanning 25 to 35 mi (40 to 56 km) and the smaller only 5 mi (8.0 km), signalling the start of an eyewall replacement cycle--the inner violent core remained undisrupted through the afternoon . Maria attained its peak intensity around 04: 00 UTC on September 20, roughly 30 mi (45 km) south of St. Croix . Sustained winds reached 175 mph (280 km / h) and its central pressure bottomed out at 908 mbar (hPa; 26.85 inHg); this ranks it as the tenth-most intense Atlantic hurricane since reliable records began . </P> <P> The hurricane made its closest approach to St. Croix around 05: 00 UTC on September 20, passing within 20 mi (30 km) of the island; the storm's outer eyewall lashed the island while the more violent inner eye remained offshore . Hours later, around 08: 00 UTC, the outer eyewall struck Vieques, an island off the eastern coast of Puerto Rico . By this time, the outer eye became dominant as the inner one decayed, and the eyewall replacement cycle caused Maria to weaken to Category 4 strength . Maria made landfall just south of Yabucoa, Puerto Rico, around 10: 15 UTC with sustained winds of 155 mph (250 km / h), making it the strongest to hit the island since the 1928 San Felipe Segundo hurricane . Maria maintained a general west - northwest course across Puerto Rico, emerging over the Atlantic Ocean shortly before 18: 00 UTC . Interaction with the mountainous terrain resulted in substantial weakening; sustained winds fell to 110 mph (175 km / h) and the central pressure rose to 957 mbars (hPa; 28.26 inHg). With favorable environmental conditions, Maria steadily reorganized as it moved away from Puerto Rico . A large eye, 45 mi (75 km) wide, developed with deep convection blossoming around it . Early on September 21, the system regained Category 3 intensity . </P> <P> Initially, cooler waters stirred up by Hurricane Irma two weeks prior limited Maria's reorganization . During the afternoon of September 21, the system traversed the Navidad and Silver banks north of the Dominican Republic; shoaling from the region's shallow waters temporarily interfered with measurements of surface winds . Convection around the storm's eye deepened and its eye became better defined that night, and the hurricane reached a tertiary peak with sustained winds of 125 mph (205 km / h). An increase in southwesterly wind shear prompted gradual weakening of the hurricane, starting with restriction of banding features and later degradation of the eyewall . Late on September 22, the hurricane turned north - northwest as it reached the western periphery of the ridge previously steering it northwest . Maria fluctuated in organization throughout September 23, with its eye periodically clearing and becoming cloud - filled; it maintained Category 3 hurricane strength during this phase . Despite a decreasing central pressure, the storm finally weakened to Category 2 strength early on September 24 . Hurricane Hunters observed flight - level winds of 116 to 135 mph (187 to 217 km / h); however, surface wind returns by the NOAA's Stepped - Frequency Microwave Radiometer were only 90 mph (150 km / h). This indicated below - average mixing down of winds aloft . By this time, Maria's trajectory shifted almost due north between the aforementioned ridge and a cut - off low over the eastern Gulf of Mexico . </P>

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