Super Typhoon Parma threatens the Philippines; October hurricane season outlook

It's been a terrible week for natural disasters in Asia, with the death toll from two huge earthquakes and Typhoon Ketsana continuing to mount. The bad news got worse today with the emergence of Super Typhoon Parma, now poised strike the northern portion of the Philippines' Luzon Island as a Category 4 typhoon with 150 mph winds. Also of concern is Category 3 Typhoon Melor, which has just undergone a period of rapid intensification, and is also approaching super typhoon status. A super typhoon is a storm with 150 mph winds or higher--a strong Category 4. Melor is forecast to pass through the northern Marianas Islands north of Guam and Saipan this weekend, then curve to the north and threaten Japan next week.

Super Typhoon Parma intensified dramatically early this morning, forming a tiny "pinhole" eye (Figure 1) only seen in very intense tropical cyclones. The last Atlantic hurricane to form a pinhole eye was Hurricane Wilma, the strongest Atlantic hurricane of all time. Parma's outer spiral bands are already beginning to spread over the eastern positions of the Philippines, and beginning Friday will likely bring 2 - 4 inches of rain to the regions hard-hit by Typhoon Ketsana, including the capital of Manila. More seriously, the super typhoon may make landfall along the northeastern portion of Luzon Island in the Philippines on Saturday as a Category 4 or 5 typhoon. The uncertainty in the forecast is very high, as steering currents are expected to weaken on Friday, and the presence of Typhoon Melor to the northeast introduces an additional element of uncertainty. It is quite possible that Parma will stall near or just offshore the northern coast of Luzon Saturday through Sunday as a super typhoon, dumping rainfall in excess of a foot over northern Luzon, as forecast by the ECMWF model. Northern Luzon received 2 - 4 inches of rain from Typhoon Ketsana last week, and an additional 12+ inches of rain falling on soils already saturated from Ketsana's rains would likely cause severe flash flooding and major landslides capable of killing hundreds. Another dismal possibility is offered by the NOGAPS model, which forecasts that Parma will cross directly over Luzon north of Manila, bringing heavy rains in excess of six inches to Manila, where more than 16 inches of rain fell Saturday during Typhoon Ketsana. It is also possible that Parma will miss the Philippines, staying far enough offshore that the Philippines will not suffer a major flooding disaster. However, the odds current favor another major typhoon disaster for the Philippines this weekend.


Figure 1. Super Typhoon Parma at 02:25 UTC on 10/01/09. Parma had developed a tiny pinhole eye, and the outer spiral bands were beginning to affect the eastern Philippines. Image credit: NASA.

October hurricane outlook
In the first half of October, Atlantic tropical cyclone activity remains quite high, before a sharp drop occurs around October 15. Since the current active hurricane period began in 1995, the first half of October has given birth to an average of 1.9 named storms, 0.7 hurricanes and 0.4 intense hurricanes. For the entire month of October, these figures are 3.9 named storms, 1.2 hurricanes, and 0.6 intense hurricanes. These numbers are about double the long-term climatological averages for the past 100 years.

The most typical track for October hurricanes is through the Western Caribbean, with recurvature to the north and northwest into the Gulf of Mexico or across Cuba and through the Bahamas. The jet stream becomes more active and moves further south in October, making recurving storms more likely, and eliminating long-track Cape Verdes-type hurricanes from making direct strikes on the U.S. East Coast or Texas. There have only been nine hurricanes that have hit the U.S. East Coast north of Miami in October or later, and only three on the Texas coast. For the U.S., the highest risk areas for an October hurricane strike are between central Louisiana and Southeast Florida. About 71% of the 53 hurricanes that have hit the U.S. after October 1 have struck this region. Here is a breakdown of the number of hurricane strikes by state between 1851 - 2008 occurring October or later:

Texas 3
Louisiana 9
Mississippi 2
Alabama 0
Florida Gulf Coast 25 (7 of these in the Panhandle)
Southeast Florida 3
Georgia 2
South Carolina 3
North Carolina 4
New England 2

There have been no direct strikes by hurricanes on the east coast of Florida north of Miami in October or later. However, the east coast of Florida is still capable of getting damaging hurricane conditions from storms that strike the Gulf Coast of Florida and move eastwards, as Hurricane Wilma of 2005 proved.


Figure 2. Tracks of all hurricanes and tropical storms forming October 1 - 15, 1851 - 2006.

There are no threat areas in the Atlantic to discuss today, and none of the computer models are forecasting tropical storm formation over the next seven days. However, the last few runs of the 16-day GFS model forecast for wind shear have been predicting a decline in wind shear over the Caribbean after October 12, so there may be a greater chance of tropical storm formation as we head into mid-October. Sea Surface Temperatures (SSTs) are certainly warm enough to support a major hurricane anywhere in the tropical Atlantic or Gulf of Mexico, and are more than 1°C above average (Figure 3).


Figure 3. Departure of Sea Surface Temperature from average for October 1, 2009. SSTs were about 1°C above average over the tropical Atlantic and Gulf of Mexico. Note the very warm anomalies over the East Pacific off the coast of South America, the signature of an El Niño event. Image credit: NOAA/SSD.

Wind shear
Wind shear has been much above average over the tropical Atlantic over the past month, which is typical for an El Niño year, though part of this shear is due to the above-average number of upper-level troughs of low pressure over the Atlantic this hurricane season. El Niño conditions in the Eastern Pacific have remained essentially unchanged over past few weeks, and are expected to intensify in the coming months, so we can expect a continuation of above-average wind shear over the Atlantic for the remainder of hurricane season. Wunderblogger Weather456 has posted a nice October hurricane outlook that goes into a bit more detail than I've done here for those interested.

The forecast
The last Atlantic hurricane season that was this quiet was the strong El Niño year of 1997. That year, we got two weak 45-mph tropical storms in October to finish out the season. I predict that for this season, we will also finish out the year with two more named storms, with one of these reaching hurricane strength. The most likely land areas such a storm might affect are along the Western Caribbean, Gulf Coast of Florida, and the Bahamas. The most likely time these storms may form is the period October 13 - November 7.

Jeff Masters