Otto Becomes a Hurricane, Watches and Warnings Issued

Tropical Storm Otto intensified into a hurricane on Tuesday as it meandered over the southwestern Caribbean Sea.  At 4:00 p.m. EST on Tuesday the center of Hurricane Otto was located at latitude 10.5°N and longitude 79.6°W which put it about 235 miles (375 km) east of Limon, Costa Rica.  Otto was moving toward the west at 2 m.p.h. (3 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 984 mb.

Hurricane Watches have been issued for the portion of the coast from the Costa Rica/Panama border to Bluefields, Nicaragua.  Tropical Storm Warnings have been issued for the portion of the coast from Nargana to Colon, Panama and for San Andres Island, Colombia.  Tropical Storm Watches have been issued for the portions of the coast from Colon, Panama to the Panama/Costa Rica border and from Bluefields to Sandy Bay Sirpi, Nicaragua.

The inner core of Hurricane Otto became more circular and symmetrical on Tuesday.  An eyelike feature appeared on microwave satellite imagery and hints of an eye were seen intermittently on visible imagery during the day.  There appeared to be breaks in the eyewall on the southeast side of the eye.  Most of the stronger thunderstorms are forming northwest of the eye.  Convective activity outside the core of Hurricane Otto is more asymmetrical.  There are some thinner rainbands north and west of the center where winds from a high pressure system are converging into the circulation of Otto.  There are fewer showers and thunderstorms in the southeastern quadrant of the circulation.  Thunderstorms around the center of the hurricane are generating upper level divergence at the very top of the circulation.

Hurricane Otto has a very small circulation.  Winds to hurricane force only extend out about 10 miles (15 km) from the center of circulation.  Winds to tropical storm force only extend out about 70 miles (110 km) from the center.  The Hurricane Intensity Index (HII) for Otto is 10.4.  The Hurricane Size Index (HSI) is 3.2 and the Hurricane Wind Intensity Size Index (HWISI) is 13.6.

Hurricane Otto will be moving through an environment that will be favorable for intensification.  It will move over water where the Sea Surface Temperature is 29°C.  An upper level ridge located east of Otto is generating southeasterly winds which are blowing against the upper portion of the circulation of the hurricane.  Those winds appear to be hitting Otto just under the level of upper level divergence at the top of the circulation.  So, the upper level winds and vertical wind shear appear to be restricting upper level divergence to the south of the circulation, but they do not appear to be completely blocking divergence.  The speed of the upper level winds is forecast to decrease.  If the vertical shear decreases, then Hurricane Otto could strengthen.

A ridge of high pressure is forecast to build north of Hurricane Otto.  That ridge will steer Otto toward the west and the hurricane could start to move faster on Wednesday.  On its anticipated track Hurricane Otto could approach the coast of Costa Rica and Nicaragua on Thursday.

Hurricane Otto is a small hurricane, but it could cause localized minor wind damage.  Heavy rain, flash floods and mudslides are a much greater threat.  Hurricane Otto could bring flooding rains to portions of Nicaragua, Honduras, Panama, Costa Rica, Guatemala and El Salvador.

On a historical note Hurricane Martha formed during this time of year in 1969 in almost exactly the same area where Hurricane Otto formed.  Hurricane Martha moved southward and weakened.  Martha officially made landfall in Panama as a tropical storm, but it did cause flooding rains and fatalities in parts of Costa Rica.