NHC/TAFB Offshore Forecast Reform

GMZ013 was designed in part to represent the Bureau of Ocean Energy Management’s Gulf of Mexico Central Planning Area for the oil and gas industry. There has been an increase in deep water drilling in this area over the past 20 to 30 years (such as the Deep Water Horizon). Deep water drilling operations are very weather sensitive. By dividing GMZ013, we would be providing more precise wording in the forecast, thus increasing the safety margin for these operations. 

Another important consideration for zones over the southeastern Gulf is the Loop Current and its eddies, where warmer water moves from the Caribbean Sea through the Yucatan Channel and into the southeast and south-central Gulf. Not only does this enhance winds and seas in this area, it supports increased showers and thunderstorms. The Florida Current extends eastward, into the Straits of Florida. This flows against the prevailing easterly winds, often resulting in higher wave heights.

Splitting GMZ019 along 91W forms the proposed zones GMZ045 and GMZ046. The easternmost zone, GMZ047, has lighter average winds overall, but also can be impacted more by eddies emerging off the Loop Current.

Over the eastern Gulf, the proposed southern boundary of GMZ015 is modified to be flush with the other two northern Gulf zones at 26N. The resulting zone, GMZ057 aligns with WFO Tampa marine zones, and GMZ047 roughly aligns with the WFO Miami and WFO Key West Gulf marine zones.

GMZ057 is more prone to impacts from cold fronts during the winter months than is GMZ047.

Meanwhile, the combined effects of the Loop Current and the Florida Current are most profound on GMZ047, occasionally supporting sea heights higher than neighboring zones particularly in the Florida Straits.

AMZ013 is split along 20N to better resolve cold fronts/shear lines and to capture occasional fresh to strong northeast winds on the leeside of Cuba. 

The southern half of AMZ013 is divided along 80W to isolate winds and seas between Jamaica and Cuba, and to better resolve winds and seas near and west of Grand Cayman Island.

The two new zones that result from this division would align with zones already established along 80W farther south. Cold fronts/shear lines often straddle this area during the dry season. 

These divisions result in three new proposed zones: AMZ041, AMZ042, and AMZ043.

Swipe the map to the right to compare the current and proposed zones in this area.

AMZ021, AMZ023, AMZ031 and AMZ033 are very large zones in the central Caribbean that usually experience a standard trade wind pattern. However, the speed of the trade winds vary greatly across this region, with frequent strong to gale force winds noted off the coast of Colombia and in the Gulf of Venezuela, and occasionally off the southern coast of Hispaniola. In addition, there is a pronounced swell gradient from east to west due to the trade wind flow and long fetch. There are major shipping lanes through this area to and from the Panama Canal, to include oil and liquified natural gas tankers maneuvering through the various islands and reefs north of Venezuela. Smaller zones offer more precise wording and are better suited to this large and diverse region. AMZ021 and AMZ31 are each split along 76W, near the eastern tip of Jamaica and aligning with the Windward Passage zone farther north. AMZ023 and AMZ033 are each split along 68W. This aligns with the western edge of the NWS San Juan office’s coastal waters area in the Mona Passage. North of 15N, this provides distinct offshore zones to Jamaica, Haiti, the Dominican Republic and Puerto Rico/Virgin Islands. South of 15N, this division keeps Aruba, Curacao, and Bonaire in the same offshore zone, while better handling the variations in weather along the coasts of Colombia and Venezuela.

AMZ039 off Panama is divided along 80W, in line with zones already established to the north, and nicely splitting the zone near the Panama Canal. The eastern half of this zone occasionally experiences surges of the strong winds funneling off Colombia.

Major sea lanes are depicted as blue lines on the proposed map to the right. Vessels transiting between the Panama Canal and Windward and Mona Passages typically move across the waters off eastern Panama, while those vessels transiting between the Canal and the Yucatan Channel go through the waters off western Panama.

The monsoon trough often bisects this area from east to west, with SW winds south of the monsoon trough and SE or NE winds to the north of the trough. With the existing large zone, it is challenging to describe both the differences in winds or seas north to south across the monsoon trough while also differentiating winds and seas from east to west. Splitting the zone along 80W alleviates this, resulting in forecast wording that will typically focus on the north-south changes across the monsoon trough.

This proposal also includes eight new zones, covering the region from 22N to 31N between 55W and 65W. These new zones may serve any traffic between the Leeward Islands and Bermuda. This is an active area during hurricane season, where Cape Verde systems occasionally recurve. Subtropical storms and upper lows are active in this area as well.

The wind speed climatology shows a distinct gradient between the relatively light wind along the subtropical ridge and stronger winds farther north associated with low pressure systems moving west to east from the east coast of the U.S. through the western Atlantic. 

Further splitting the existing northern zones along 29N accounts for this natural division, resolving the stronger winds north of the subtropical ridge. Furthermore, splitting the zones along 25N, usually will differentiate easterly winds south of the ridge from westerly winds north of the ridge.

Subdividing the existing zones further along longitude lines will better resolve frontal boundaries entering the area from the northwest, as well as any tropical cyclone moving through the region.

Dividing AMZ111 along 29N roughly correlates with the border between WFO Jacksonville and WFO Melbourne to the west, and OPC to the north. The more detailed output that would result from dividing AMZ111 would also be more consistent with the neighboring marine zones.

Dividing AMZ113 along 74W would account for the more active weather noticed in the western half of this zone. This is due to a combination of the aforementioned gradient along with the warmer waters of the Gulf Stream allowing efficient mixing of higher momentum winds to the surface. This is also an area where short wave troughs occasionally dig southeastward before lifting to the north. Finally, the western half of AMZ113 becomes the proposed zones AMZ064 and AMZ070. AMZ064 would border the neighboring OPC zone to the north. 

AMZ117 is split along 24N, essentially splitting the northern Bahamas from the central Bahamas. This division would allow more precise wording during tropical cyclone events.

AMZ119 and AMZ121 are split along 25N, enabling the formatter to better define the winds around the subtropical ridge.

Tight pressure gradients are common in this area, with very light winds near the ridge axis, not very far from relatively strong trade winds to the south. This division will help better resolve these details.