A tropical cyclone could potentially develop over the Southwestern Caribbean Sea during the next week. An area of low pressure is expected to form near the surface over the Southwestern Caribbean Sea during the next few days. The low pressure system will form in an environment that will be favorable for the development of a tropical cyclone. The low pressure system will form over water where the Sea Surface Temperatures are near 30°C. It will form under an upper level ridge that will be over the Southwestern Caribbean Sea. The upper level winds will be weak in the ridge and there will be little vertical wind shear. The low pressure system could gradually organize into a tropical cyclone. The U.S. National Hurricane Center is indicating that the probability is 30% that a tropical cyclone forms over the Southwestern Caribbean Sea during the next seven days.
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NHC To Extend Tropical Weather Outlook to Seven Days in 2023
The National Hurricane Center (NHC) stated that it will extend the length of the period covered by the Tropical Weather Outlook (TWO) from five to seven days in 2023. Both the textual and graphical outlooks will be extended to seven days. NHC also indicated that it will begin to include invest numbers in the Tropical Weather Outlook, when it is appropriate.
NHC is going to remove information on land based tropical cyclone watches and warnings from the Tropical Cyclone Forecast/Advisories. NHC will continue to provide information on land based tropical cyclone watches and warnings in the Tropical Cyclone Public Advisories.
NHC will make the Peak Storm Surge Forecast graphic operational in 2023. The Peak Storm Surge Forecast graphic provided in previous years was considered experimental.
The Peak Storm Surge Flooding Map issued by NHC will now also be issued for Puerto Rico and the U.S. Virgin Islands.
Possible Subtropical Development Southeast of Bermuda
A low pressure system southeast of Bermuda could develop into a subtropical storm during the next few days. At 9:00 a.m. EST on Monday the center of the low pressure system was located at latitude 24.0°N and longitude 55.0°W which put it about 855 miles (1380 km) southeast of Bermuda. The low pressure system was moving toward the north at 5 m.p.h. (8 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1005 mb.
A low pressure system southeast of Bermuda has the potential to develop into a subtropical storm this week. There is already a strong surface circulation around the low pressure system. The surface low pressure system is located northeast of an upper level low. Bands of showers and thunderstorms were occurring in the northern and eastern parts of the surface low pressure system. Bands in the southern and western parts of the surface low consisted primarily of showers and lower clouds.
The low pressure system southeast of Bermuda will move through an environment somewhat favorable for the development of a subtropical storm during the next 48 hours. The low pressure system will move over water where the Sea Surface Temperatures are near 26˚C. It will move under the northeastern part of an upper level low. The upper level low will produce southeasterly winds that will blow across the top of the surface low. Those winds will cause some vertical wind shear. The vertical wind shear will likely make the environment unfavorable for the development of a tropical storm. However, the wind shear may be weak enough to allow for the surface low to make a transition to a subtropical storm. The National Hurricane Center is indicating there is a probability of 40% that the surface low pressure system develops into a subtropical storm during the next five days.
The upper low will steer the surface low pressure system slowly toward the northwest during the next 48 hours. On its anticipated track the surface low pressure system will remain far to the southeast of Bermuda.
Cluster of Thunderstorms Forms over Central Gulf of Mexico
A cluster of thunderstorms formed over the central Gulf of Mexico on Saturday. The cluster of storms persisted on Sunday morning. At 8:00 a.m. EDT on Sunday the center of the cluster of thunderstorms was located near latitude 26.0°N and longitude 88.0°W which put it about 310 miles (500 km) south of Mobile, Alabama. The cluster of thunderstorms was moving slowly toward the north-northeast. Some of the thunderstorms in the cluster were producing sustained winds of 35 m.p.h. (55 km/h) and and there were wind gusts to 45 m.p.h. (75 km/h). The minimum surface pressure was 1015 mb.
A cluster of thunderstorms formed over the central Gulf of Mexico on Saturday and it persisted on Sunday morning. There was not a well defined low level center of circulation beneath the cluster of storms. Visible satellite loops provided indications of several possible centers of rotation in the middle troposphere. Thunderstorms in the cluster generated some upper level divergence that pumped mass away toward the northeast. The strongest winds were occurring in bands of thunderstorms.
The cluster of thunderstorms will move through an environment that will be marginally favorable for the development of a tropical cyclone during the next 18 hours. The cluster of storms will move over water where the Sea Surface Temperatures are near 29˚C. The southern end of an upper level trough over the central U.S. will produce southwesterly winds that will blow toward the top of the thunderstorms. Those winds will cause some vertical wind shear and the wind shear will inhibit the development of a tropical cyclone. The cluster of thunderstorms is currently forecast not to develop into a tropical cyclone, but some development could occur if a surface center of circulation forms beneath the cluster.
The upper level trough over the central U.S. will steer the cluster of thunderstorms toward the north-northeast. On its anticipated track the cluster of storms will move toward the central Gulf Coast. Bands of thunderstorms could drop locally heavy rain over northwest Florida and south Alabama during the next 48 hours. One band of showers and thunderstorms is currently approaching that area. Heavy rain could cause flash floods in some locations. Some thunderstorms could approach severe criteria.
New Normals for Atlantic Hurricane Season
The National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center (CPC) announced that new normals have been computed for the Atlantic Hurricane season. CPC will now use normals based on the averages for the thirty year period from 1991-2020. The new normal number of named storms for the Atlantic basin is 14. The new normal for hurricanes is 7 and the normal for major hurricanes is 3.
Climatologists routinely calculate new normals based on the most recent 30 year period at the end of each decade. The previous normals for the Atlantic basin were based on the period from 1981 to 2010. The previous normal for the number of named storms was 12. The previous normal for the number of hurricanes was 6 and the previous normal for the number of major hurricanes was 3. The increases in the number of named storms and hurricanes reflect a more active period that began in 1995.
Possible Development Near the Bahamas
A low pressure system could develop near the Bahamas on Friday or Saturday. The National Hurricane Center is indicating that there is a 70% probability that the low pressure system could develop into a subtropical cyclone.
A stationary frontal boundary extends from south of Florida across the Bahamas. A small upper level trough called a shortwave over the southwestern U.S. will move east toward the stationary front later this week. When the upper level trough approaches the stationary front, a low pressure system is likely to develop near the Bahamas. If thunderstorms develop near the center of the low pressure system, then it could exhibit the structure of a tropical or subtropical cyclone. The Sea Surface Temperature near the Bahamas is near 26°C. So, the water will be warm enough to support the development of a tropical cyclone. However, the winds blowing around the upper level trough will cause moderate vertical wind shear. The wind shear may be strong enough to inhibit the development of a tropical cyclone. However, the shear may not be strong enough to prevent the development of a subtropical cyclone. If the low pressure system strengthens into a subtropical storm, it will be designated Subtropical Storm Arthur.
System Could Bring Heavy Rain to Southeast U.S.
A weather system over the southeastern Gulf of Mexico could bring heavy rain to the southeastern U.S. this week. An upper level low over the eastern Gulf of Mexico could transfer enough kinetic energy down to the lower troposphere to spin up a low at the surface. Air flowing around the eastern side of the low is contributing to upper level divergence over Florida. The divergence enhanced rising motion over Florida and rain fell over parts of the southern and central portions of that state.
The weather system is forecast to move slowly northward during the next several days. The Sea Surface Temperatures in the southeastern Gulf of Mexico are 24°C to 26°C. There is enough energy in the upper levels of the water to support the formation of a tropical cyclone. The upper level low will create southerly winds which will cause moderate vertical wind shear. The shear will inhibit development, although those winds could contribute to upper level divergence to the east of the weather system. Upper level divergence could allow the surface pressure to decrease and a low pressure system could form at the surface. The National Hurricane Center (NHC) issued a special Tropical Weather Outlook on Sunday afternoon on the weather system. NHC indicated the probability was 40% that a tropical or subtropical cyclone could form during the next five days.
Guidance from numerical models suggest that the weather system will move slowly northward over the eastern Gulf of Mexico during the next few days. Counterclockwise rotation around the low will transport moist air northward on the eastern side of the low. The moist air combined with upper level divergence will create the potential for locally heavy rainfall over the southeastern U.S. Heavy rain could result in floods in some locations.
System to Bring Wind, Rain to Bahamas and South Florida
A complex weather system near the Bahamas is forecast to move westward and it will bring gusty winds and locally heavy rain to parts of the Bahamas and South Florida during the weekend. The circulation is strongest in the middle and upper troposphere. An upper level low is centered near the Bahamas. Showers and thunderstorms are occurring north and east of the upper low. There is not a distinct center of circulation in the lower troposphere or at the surface. There is a small upper level ridge to the east of the upper low and the ridge is producing some upper level divergence which is pumping mass away to the east of the system.
The system will move through an environment that is only marginally favorable for the development of a tropical cyclone. It will move over water where the Sea Surface Temperature is near 26°C. So, there is potentially enough energy in the upper ocean to support the development of a minimal tropical cyclone. The upper low and the ridge to the east are southerly winds near the Bahamas and westerly winds southeast of the Bahamas. Those winds are causing strong vertical wind shear. The winds are weaker near the center of the upper low, but there are no thunderstorms in that region at the current time. If a surface low were to develop under the center of the upper low, then there would be the possibility of some slow development. A second, possible scenario is that a subtropical cyclone develops north and east of the upper low where the showers and thunderstorms are forming.
The National Hurricane Center (NHC) issued a special Tropical Weather Outlook on this system at 10:45 a.m. EDT on Friday. NHC indicated that “no significant development” is expected and it gives a 0% probability of the formation of a tropical cyclone.
The upper level low is forecast to move south-southwest over the northwestern Caribbean Sea during the next 72 hours. The surface and lower parts of the system are forecast to move across the Bahamas toward South Florida during the weekend. Since the showers and thunderstorms are occurring north and east of the upper low, this could bring gusty winds and locally heavy rain to parts of the Bahamas and South Florida during the weekend. Some of the humid air on the northeastern periphery of the system could be pulled toward the Carolinas ahead of an approaching cold front. The moist air could enhance rainfall in eastern South Carolina and eastern North Carolina when the cold front moves through those places and lifts the air.