The threat posed by a low pressure system over the Southwestern Caribbean Sea prompted the issuance of a Tropical Storm Warning for Jamaica and a Hurricane Watch for the Cayman Islands on Sunday afternoon.  The low pressure system was designated as Potential Tropical Cyclone Eighteen by the U.S. National Hurricane Center.  At 4:00 p.m. EST on Sunday the center of Potential Tropical Cyclone Eighteen was located at latitude 13.0°N and longitude 77.1°W which put the center about 345 miles (555 km) south of Kingston, Jamaica.  The low pressure system was moving toward the northeast at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1004 mb.

A Hurricane Watch is in effect for Grand Cayman, Little Cayman, and Cayman Brac.

A Tropical Storm Warning is in effect for Jamaica.

A U.S. Air Force Reserve Hurricane Hunter aircraft investigated a low pressure system over the Southwestern Caribbean Sea on Sunday afternoon.  The aircraft found that there was a distinct low low level center of circulation in the low pressure system.  More thunderstorms were forming near the center of the low pressure system.  Bands of showers and thunderstorms were starting to revolve around the center of Potential Tropical Cyclone Eighteen.  Storms near the center of the low pressure system began to generate upper level divergence.

Potential Tropical Cyclone Eighteen will move through an environment favorable for intensification during the next 24 hours.  The low pressure system will move over water where the Sea Surface Temperatures are near 29°C.  It will move under the western end of an upper level ridge over the Caribbean Sea.  The upper level ridge will produce southeasterly winds that will blow toward the top of the low pressure system.  Those winds will cause some vertical wind shear, but the wind shear will not be enough to prevent intensification.  Potential Tropical Cyclone Eighteen will intensify during the next 24 hours.  It is likely to become a tropical storm on Monday.

Potential Tropical Cyclone Eighteen will move around the southwestern part of a high pressure system over the western Atlantic Ocean.  The high pressure system will steer Potential Tropical Cyclone Eighteen toward the north-northwest during the next 24 hours.  On its anticipated track, Potential Tropical Cyclone Eighteen will reach Jamaica on Monday night.  It could reach the Cayman Islands on Tuesday afternoon.

Potential Tropical Cyclone Eighteen will bring strong winds and heavy rain Jamaica and the Cayman Islands.  Heavy rain is likely to cause floods in some locations.

Elsewhere, Subtropical Storm Patty moved east of the Azores.  At 4:00 p.m. EST on Sunday the center of Subtropical Storm Patty was located at latitude 37.3°N and longitude 22.3°W which put the center about 280 miles (450 km) east-southeast of Lajes, Azores.  Patty was moving toward the east at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 990 mb.