WunderBlog Archive » Category 6™

Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.

Tropical Storm Paula forming

By: Dr. Jeff Masters, 7:30 PM GMT on October 11, 2010

Data from the Hurricane Hunters, land stations, and satellite imagery reveal that the strong tropical disturbance centered near the coast of Honduras just west of the border with Nicaragua is now Tropical Storm Paula. Paula is the 16th named storm of the 2010 Atlantic hurricane season. The Hurricane Hunters reported a central pressure of 1001 mb and top surface winds of 45 mph in their 2:11pm EDT center fix. Satellite imagery shows a well-organized system with a modest but increasing amount of intense thunderstorm activity, and some respectable low-level spiral bands. Water vapor satellite loops reveal that Paula has been able to substantially moisten the atmosphere in the Western Caribbean over the past day, and dry air will be less of an impediment to development than it was yesterday. Wind shear is a moderate 10 - 15 knots. Puerto Lempira, Honduras reported sustained winds of 35 mph at 12pm CST this afternoon, with 3.31" of rain from the storm thus far.

Figure 1. Afternoon satellite image of Paula.

Forecast for Paula
Proximity to land is hampering Paula's ability to intensify some, and the storm's northwest movement of 10 mph will take the center far enough away from the coast of Honduras this evening to substantially increase the storm's ability to intensify. The latest SHIPS model forecast calls for wind shear to stay mostly in the moderate range, 10 - 15 knots, through Tuesday afternoon, then increase to the high range, 20 - 25 knots, for the remainder of the week. The computer models predict Paula will continue on a northwest motion then turn more north-northwest on Wednesday, which would take the storm close to landfall on the coast of Belize or Mexico's Yucatan Peninsula Tuesday night or Wednesday morning. At that time, Paula may be approaching Category 2 hurricane status, due to the moderate wind shear, SSTs of 29°C, and a sufficiently moist atmosphere. On Wednesday, there is considerable doubt about the future path of Paula. Steering currents in the Western Caribbean will collapse, potentially allowing Paula to wander in the region for many days, as predicted by the GFS and HWRF models. It is also possible that Paula will push far enough inland over Mexico's Yucatan Peninsula that the storm will dissipate, as predicted by the NOGAPS model. Finally, if Paula grows strong quickly, and pushes far enough north, it could get caught up a strong trough of low pressure predicted to traverse the U.S. this week (and spawn a Nor'easter for New England this weekend.) In this scenario, offered by the GFDL model, Paula would make a sharp turn to the east-northeast, hit western Cuba, bring tropical storm-force finds to the Florida Keys on Thursday, then move into the Bahama Islands by Friday or Saturday. It is too early to say which of these scenarios is the most likely, as the storm is just forming and the models do not have a good handle on it yet. Regardless, northern Honduras, Belize, and Mexico's Yucatan Peninsula will receive dangerous flooding rains from Paula today through Wednesday.

The U.S. drought in major hurricanes
On average, the U.S. gets hit by one major Category 3 or stronger hurricane every two years. This year, the team of hurricane forecasters at Colorado State University called for a 76% chance of a major hurricane hitting the U.S. in their June forecast. However, the odds of a major hurricane hitting the U.S. are rapidly dwindling. Over the past fifty years, the only Category 3 or stronger hurricanes to hit the U.S. after October 1 were Hilda (October 3, 1964), Opal (October 4, 1995), and Wilma (October 24, 2005). Hilda and Opal were already named tropical storms as of October 1, so Wilma was the major hurricane that formed after October 1 to hit the U.S. during this period. Although we still need to keep a wary eye on developments in the Western Caribbean over the next few weeks, the odds are that 2010 will join 1951 as the only year to have five or more major hurricanes in the Atlantic, but no landfalling major hurricane in the U.S. (1958 is also listed as such a year, but a re-analysis effort is showing that Hurricane Helene hit North Carolina as a major hurricane that year.) If 2010 finishes without a major hurricane hitting the U.S., this will mark the first such five-year stretch since 1910 - 1914.

Figure 2. Hurricane Wilma over South Florida as a Category 3 hurricane on October 24, 2005. Wilma was the last major hurricane to hit the U.S.

However, some caveats are required. Hurricanes Gustav and Ike, which both made landfall in the U.S. in 2008 as top-end Category 2 storms with 110 mph winds, would probably have been classified as Category 3 hurricanes had they occurred early in the 20th century. This is because in past, when there were not any reliable wind measurements in the vicinity of a landfalling hurricane (a common occurrence), the storm was classified based on its central pressure. Gustav and Ike had central pressures of 957 and 952 mb, respectively, which would have qualified them as Category 3 storms. Similarly, Hurricane Floyd of 1999 and Hurricane Isabel of 2002 (though not within the last five years) were strong Category 2 hurricanes with 105 mph winds at landfall, but had central pressures of 956 mb. These hurricanes would also have been classified as Category 3 hurricanes in the past. There are many storms from the 1930s, 1940s, and 1950s that will likely change their landfall classification once re-analysis efforts are completed over the next few years. One case is Hurricane Ten of 1949, which is listed as having winds of a low-end Category 4 hurricane (135 mph) just before landfall, which would make it the only October major hurricane to make landfall in Texas. However, the hurricane is only given a Category 2 strength at landfall, based on its central pressure.

Prior to 1960, there were five major hurricanes that hit Florida in October. Most notable of these is Hurricane King, which hit downtown Miami on October 18, 1950, as a Category 3 hurricane.

Record quiet hurricane and typhoon seasons in the Pacific
Over in the Western Pacific, it is currently the quietest typhoon season on record, according to statistics computed by forecaster Paul Stanko at the NWS office on Guam. On average, by this point in the season, there should have been 21 named storms, 13 typhoons, and 3 supertyphoons (storms with 150+ mph winds.) So far in 2010, there have been just 12 named storms, 6 typhoons, and no supertyphoons. The record lows for the Western Pacific (since 1951) are 18 named storms, 9 typhoons, and 0 supertyphoons. We have a good chance of beating or tying all of those records. Over the in the Eastern Pacific, it has also been a near record-quiet season. On average, the Eastern Pacific has 15 named storms, 8 hurricanes, and 3 intense hurricanes in a season. So far in 2010, there have been 7 named storms, 3 hurricanes, and 2 intense hurricanes. The record quietest season since 1966 was the year 1977, when the Eastern Pacific had 8 named storms, 4 hurricanes, and 0 intense hurricanes. Climatology suggests that on average, we can expect just one more named storm in the Eastern Pacific this late in the season, so there is a good chance that the 2010 season is over. La Niña is largely responsible to the quiet Eastern Pacific hurricane season, due in part to the cool sea surface temperatures it brought. La Niña also commonly causes less active Western Pacific typhoon seasons, since the warmest waters there shift closer to Asia, reducing the amount of time storms have over water.

I'll have an update Tuesday morning at the latest.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.