The NWS International Activities Office (IAO) administers international agreements with nine countries in support of ten upper air stations as part of the Cooperative Hurricane Upper-Air Stations (CHUAS) network in the Caribbean basin. These observations are extremely important not only to the forecasters of the National Hurricane Center (NHC) but also to each participating Caribbean country in support of its hurricane forecasting activities and to provide data for research.
These stations are located on the Caribbean islands of Bahamas, Barbados, Curaçao (Netherlands Antilles), Dominican Republic, Grand Cayman, Jamaica, San Andres (Columbia), St. Maarten (Netherlands Antilles), Trinidad, and in the Central American country of Belize.
The NWS Maintenance Branch supports the CHUAS network with technical maintenance support, both by telephone consultation and on site, and provides the day-to-day operational supplies of radiosondes and balloons.
These upper-air observations are made by balloon-borne electronic-instrument packages, which are carried aloft to an altitude of nearly 20 miles. Observations are usually made at midnight (Universal Time), although during a portion of the hurricane season, additional observations are made (see table below). Similar observations are made at hundreds of locations around the world as part of the World Meteorological Organization (WMO) Global Upper-Air Network (GUAN).
The birth of the CHUAS network occurred during the late 1950's and early 1960's. At that time, the NWS supported a Polar Operations Project, which installed and operated many upper air stations in Canada, Alaska, the Arctic, and Antarctica. Stations were also established in Mexico, many South and Central American countries, and on several Caribbean Islands.
Formal agreements with the nine Caribbean countries to support the upper-air stations were established during the period 1969 - 1985. In addition to providing equipment, spare parts and expendables, many of the CHUAS stations required an on site U.S. technician for maintenance and administration. These agreements are currently being updated to reflect the current bilateral relationship.
Originally, most of these stations used old World War II-era military-surplus ground-receiving equipment – an SCR 658, which was a radio-direction finder used to track the balloons carrying the radiosondes. The SCR-658 required manual tracking of the balloon’s flight and several highly trained people to calculate the wind and other data. Balloons were filled by hydrogen produced by a variety of high- and low-pressure gas generators. These generators were somewhat dangerous to operate and had environmentally unsound waste products.
During the 1970's, the NWS Overseas Operations Division upgraded many of these stations to surplus U.S. Air Force equipment (the GMD-5 system built by Space Data Division), which provided for automatic tracking of the balloons’ flight. Calculations were still done by manual operations. Electrolytic hydrogen generators, which produce hydrogen by passing electricity through water to separate the hydrogen and oxygen, replaced the older high- and low-pressure chemical generators. In addition, U. S. personnel returned home as the stations’ capacity for self maintenance and administration improved.
In the 1980's, the NWS IAO provided computer equipment to perform the majority of the calculations allowing for complete operation by one highly skilled operator. Some ground-receiving equipment was updated to solid-state technology, and all sites were provided with IBM PC’s to do the calculations and message-coding operations. Also, the countries became more self reliant in terms of operational and maintenance responsibilities. All stations were fully manned by local national personnel by the end of the 1980's.
In the early 1990's, the GMD equipment was replaced with modern computer-based tracking equipment using the OMEGA navigation-beacon network for upper-air wind determination. With the demise (September 1997) of the OMEGA navigation network, two of these stations, Jamaica and Bahamas, were converted to use the Loran-C beacon network while the other five stations were replaced with ATIR CV-700 equipment (modern, solid state GMD-like tracking systems).
In the early 2000’s, the day-to-day responsibilities for maintenance and operation of CHUAS were transferred to the NWS Maintenance Branch.
Beginning in 2002, the old Stuart electrolytic hydrogen generators were replaced by more modern proton-exchange systems provided by Proton Energy Systems of Wallingford, CT.
With the development of the Telemetry Receiving System (TRS) system by InterMet for the NWS Radiosonde Replacement System (RRS) program, the decision to upgrade all of the CHUAS stations to the same electronics package as the TRS was made, and the IMS-1500 system was installed at all locations. This was completed in 2003.
Currently, the National Weather Service, through the Maintenance Branch, provides consumables and limited maintenance support to the CHUAS stations.