Hurricane Julia explodes — Atlantic has two coincident Category 4 hurricanes, very rare

UPDATE 5 AM AST: Second time in 100-years two coincident Category 4’s in the Atlantic…together, Igor and Julia have the highest coincident intensities on record.

Two major hurricanes exist simultaneously in the North Atlantic, a rare occurrence.  With the current intensities (110 knots +) of Julia and Igor, this has only happened 3-times in the past 60-years:  1950 [Dog & Easy], 1958 [Helene & Ilsa], and 1999 [Floyd & Gert].  But Igor and Julia are both very powerful major hurricanes, they are Category 4’s.

• Unprecedented:  in our North Atlantic historical records, the forecast intensities of Igor and Julia during the next 12-24 hours will be unprecedented for coincident storms.  The only other time (we know of) coincident Category 4+ hurricanes occurred was in 1926 with Hurricane #4 and the Great Miami Hurricane (September 26 at 06:00 UTC).

• More:  At 115 knots +, Hurricane Julia is the most intense storm that far in the Eastern Atlantic [-31.8W] joining other major hurricane east of -35W including Frances 1980 and Fred 2009.

Hurricane Julia has rapidly intensified during the morning hours of September 15, blowing up to Category 3 + (110 knots).  Meanwhile, closer to the USA mainland, Igor was packing 135 knot winds, just the smallest of margins weaker than Category 5.  Need 136 knots, but the NHC issues advisories in increments of 5 knots.  If Igor does not break the Category 5 plateau, it is possible a post-season re-analysis will bump the storm into the most extreme Saffir-Simpson category.

ACE has really picked up:  90 as of 00Z September 15… [note the Western Pacific is 83% below normal].

Coincident major hurricanes (96 knots +) in the Atlantic basin have not occurred very often since 1950.  To ferret out the occurrences, we need to go into the best-track database.

From the HURDAT best-track database, which I have put into a easily digestible form here:  Atlantic storm listing, it is trivial with a quick UNIX/Linux command prompt:

cat hurdat_1850_2009 | awk ‘($1 >= 1950 && $8 >= 100) {print $4}’ | sort -n -k 1,1 | uniq -d

1950090406 – 1950090518

1951090712 – 1951090800

1955091806 – 1955091900

1958092618 – 1958092800

1961091112 – 1961091200

1964090918 – 1964091000

1969081806 – 1999091500

1999091506 – 1999091512

But Julia is at 110 knots and Igor at 135 knots.  Let’s then see the occurrences of 110 knots+ for two hurricanes:

1950090412

1950090418

1950090500

1958092700

1958092706

1999091506

Only 6 time-instances in the best-track since 1950!

Here are the particulars for those events:

YEAR, #, BASIN, DATE, STAGE, LAT, LON, Wind Speed (knots)

1999 09  NA 1999091506 TS  28.20  -78.50 110

1999 10  NA 1999091506 TS  17.40  -47.90 110

1958 08  NA 1958092700 TS  31.70  -78.10 110

1958 09  NA 1958092700 TS  21.40  -61.20 115

1958 08  NA 1958092706 TS  32.40  -78.50 110

1958 09  NA 1958092706 TS  21.90  -61.30 110

1950 03  NA 1950090500 ET 39.70  -56.80 55

1950 04  NA 1950090500 TS  23.40  -67.70 140

1950 05  NA 1950090500 TS  27.90  -83.10 110

1950 03  NA 1950090418 TS  38.40  -58.10 65

1950 04  NA 1950090418 TS  22.90  -67.20 135

1950 05  NA 1950090418 TS  28.00  -83.80 110

1950 03  NA 1950090412 TS  37.80  -58.80 70

1950 04  NA 1950090412 TS  22.60  -66.80 135

1950 05  NA 1950090412 TS  27.40  -83.20 110

Early September 15, Julia was at 110 knots, Igor at 135 knots, and Karl at 40 knots.