Another set of twin cyclones.:
Qhttp://satellite.ehabich.info/hurricane-watch.htm

I wonder what is going on. Is it a more common phenomenon than
previously realised or is there a glitch in the apparatus?

"The Dvorak technique (developed in 1974 by Vernon Dvorak) is a widely
used system to subjectively estimate tropical cyclone intensity based
solely on visible and infrared satellite images.

Several agencies issue Dvorak intensity numbers for cyclones of
sufficient intensity. These include the National Hurricane Center's
Tropical Analysis and Forecast Branch (TAFB), the NOAA/NESDIS
Satellite Analysis Branch (SAB), the Joint Typhoon Warning Center at
the Naval Pacific Meteorology and Oceanography Center in Pearl Harbor,
Hawaii, and the Air Force Weather Agency (AFWA).

In a developing cyclone, the technique takes advantage of the fact
that cyclones of similar intensity tend to have certain characteristic
features, and as they strengthen, they tend to change in appearance in
a predictable manner.

The structure and organization of the tropical cyclone are tracked
over 24 hours to determine if the storm has weakened, maintained its
intensity, or strengthened. Various central cloud and banding features
are compared with templates that show typical storm patterns and their
associated intensity.

If infrared satellite imagery is available for a cyclone with a
visible eye pattern, then the technique utilizes the difference
between the temperature of the warm eye and the surrounding cold cloud
tops to determine intensity (colder cloud tops generally indicate a
more intense storm).

In each case a "T-number" and a Current Intensity (CI) value are
assigned to the storm. These measurements range between 1 (minimum
intensity) and 8 (maximum intensity). The T-number and CI value are
the same except for weakening storms, in which case the CI is higher.

the list shows:
the Dvorak Number, wind speed in Knots; Pressure Millibars and the two
different ocean basins considered: the Atlantic and the North West
Pacific.

1.0 25 ---- ----
2.0 30 1009 1000
2.5 35 1005 997
3.0 45 1000 991
3.5 55 994 984
4.0 65 987 976
4.5 77 979 966
5.0 90 970 954
5.5 102 960 941
6.0 115 948 927
6.5 127 935 914
7.0 140 921 898
7.5 155 906 879
8.0 170 890 858

The National Hurricane Center will often quote Dvorak T-numbers e.g.

DVORAK SATELLITE INTENSITY ESTIMATE OF T2.5/35 KT.

The Cooperative Institute for Meteorological Satellite Studies (CIMSS)
at the University of Wisconsin-Madison has developed the Objective
Dvorak Technique (ODT). This is a modified version of the Dvorak
technique which uses computer algorithms rather than subjective human
interpretation to arrive at a CI number. This is generally not
implemented for tropical depressions or weak tropical storms."

http://en.wikipedia.org/wiki/Dvorak_techniqu"