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Posted at 01:48 PM ET, 10/12/2012

Patty forms as hurricane season enters its second maximum; and the latest on GOES-East

A disturbance that had been festering north of the Greater Antilles since October 6 was upgraded to Tropical Depression 16 yesterday morning, then quickly upgraded again to Tropical Storm Patty just six hours later. Patty is the 16th named storm of the season, and while that’s quite rare, the earliest date for reaching the 16th named storm is September 17 (Philippe in 2005). This satellite image shows Patty just north of the Bahamas and 500 miles due east of Miami... the maximum sustained winds are 40mph, and it is not expected to last much longer due to increasing shear and dry air associated with a frontal boundary. The low-level center is already exposed, with all of the thunderstorm activity displaced to the east.


(NOAA)
Another disturbance located over the Lesser Antilles is an easterly wave that left the African coast back on October 5. This stands a good chance at becoming the next named storm, Rafael, as it heads north toward Puerto Rico.

In addition to the satellite imagery, this wave is also passing over some ground-based radar sites, surface observation sites, and an Air Force reconnaissance plane will be flying through it later today. We will have as accurate of an assessment of its intensity as possible. The intensity at 8 a.m. EDT was estimated to be 40 mph with a 29.70“ (1006mb) central pressure.


Enhanced satellite image of the disturbance (“pre-TD17”, or “pre-Rafael”) over the Lesser Antilles. The approximate location of the surface center is marked with a red L. (NOAA)
The track will almost certainly take it northwest over the Virgin Islands and Puerto Rico, then north toward Bermuda. It’s fairly disorganized now, and given the environment ahead of it, it’s rather unlikely that this could become a hurricane. The biggest hazard for the eastern Caribbean mountainous islands will be flash flooding and mudslides.

Activity may pick up in the coming weeks

Climatologically, we are entering the second peak in tropical cyclone activity in the Atlantic... typically the middle two weeks of October. While the primary peak in early-mid September is by far the most significant, the late October secondary peak does exist for physical reasons. Of course, from year to year, activity doesn’t necessarily follow this average curve.


Climatological annual cycle of tropical cyclone activity in the Atlantic. Today's date is marked by the green line. (NHC - NHC)
In mid-August through late September, the entire tropical and subtropical portions of the basin are generally conducive for tropical cyclones to form. Prior to that, the sea surface temperatures are a little too cool, and the African easterly jet has not yet kicked into high gear (the source of the frequent easterly waves we discuss leaving the African coast and heading west). After that, the ocean begins to cool off, and vertical shear increases over much of the central and eastern Atlantic. But, there’s some overlap between the ocean still being warm, a stronger monsoon trough over the western Caribbean, and mid-latitude fronts and troughs reaching far enough south to spawn disturbances in the tropics and subtropics. We are currently in that unique period.

In addition to those climatological factors, other signals and oscillations (known within the weather community by an endless list of acronyms such as ENSO, MJO, NAO, AMO, etc) can influence activity on weekly and monthly timescales, and may or may not be in phase with each other or with the climatological signals. One big signal of interest in the coming weeks is the MJO, or Madden-Julian Oscillation: it’s a large region of enhanced thunderstorm activity and favorable winds that starts in the Indian Ocean and migrates around the global deep tropics every month or two. Almost all models predict that within the next 2-4 weeks, the MJO will be in a phase that favors development in the Atlantic. One leading model, ECMWF, is shown here. For a more thorough description of the plot, please refer to my previous post from September 20.


The latest two-week MJO phase forecast (green line) from the ECMWF model. (NOAA/CPC - NOAA/CPC)

GOES-East

A brief update on the GOES-East situation... some of GOES-13’s key instruments failed on September 23, and engineers have been working on a fix since then. In the meantime, GOES-14 has been pulled out of its role as a spare and has been maneuvering eastward at a rate of 0.9 degrees/day to replace GOES-13 if necessary. Starting yesterday morning and ending later this morning, GOES-13 was switched back on for a science test and quantitative evaluation. At its current rate, GOES-14 will make it to 75W by November 3 if GOES-13 isn’t fixed by then. The graphic below shows the locations of the three GOES satellites operated by NOAA prior to this event. Today, GOES-14 is centered over 95.1W, indicated by the yellow dot.


The three NOAA geosynchronous satellites: GOES-15 (West), GOES-14 (current East), and GOES-13 (former East). GOES-14 has been moving eastward since October 1 and is located at the yellow dot today. Satellites and orbits are not to scale.

* Brian McNoldy is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

By Brian McNoldy  |  01:48 PM ET, 10/12/2012

Categories:  Latest, Tropical Weather

 
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