Charles E. Roop giving his own forecasts, weather discussions, photos and adventures for the Starkville, MS area, Florida, and beyond.

Tuesday, July 20, 2010

Watching the Tropics: Invest 97L

Wow, it's been a while since I have posted any weather analysis on this blog. I've been pretty occupied for the last few weeks. My load has lightened somewhat to the point where I can sit down and write a post on weather happenings. However, things will be busy again for me soon as I prepare to move to Starkville, MS for at least the next two years for graduate studies at Mississippi State University.

So far in the Atlantic-basin hurricane season, we have had one hurricane that broke some 40-plus-year records for the month of June (Alex). We had one tropical depression, but noting noteworthy on that.

We ("we," as in "weather people") are now watching what could be our next named storm - Bonnie. A tropical disturbance, dubbed Invest 97L, is located near Puerto Rico and Hispaniola and is producing heavy rainfall in the vicinity. NWS-San Juan, PR radar estimates are showing as much as 6 to 7 inches of rain in some parts of extreme eastern Puerto Rico since Saturday. This wave has been moving west-northwestward at about 10 mph and this track is expected to continue for at least the next day or two.

Right now there is at least one feature affecting 97L: Wind shear. Remember that too much wind shear can limit a tropical cyclone's development. There is fairly light shear in the south-end of the wave (as seen here in the analysis). On the north side of the wave, shear is relatively high at 20-25 knots. Satellite imagery picks this up fairly well. This shear is due to an upper-level low, and it can also be seen in initial model runs and in water vapor imagery (see image below from NOAA).

However, the National Hurricane Center is saying that the environment around 97L should improve for further development later on. This tells me that the shear is expected to decrease at least somewhat. About half of the intensity forecast models have the invest at tropical storm status in 12 to 24 hours.

As for the track, the model consensus earlier today has the disturbance moving towards south Florida by the weekend. However, new model runs seem to have it moving a little further south, more in the Florida Keys in about 72 hours.

An area of high pressure currently has a hold over the southeastern United States. The short-term outlooks seem to have this remain in place. This should keep the invest from moving too far north, sort of acting like a blockade.

Air Force hurricane reconnaissance aircraft is scheduled to investigate the disturbance on Wednesday, if conditions still warrant (and I think it will).

Also, as other meteorologists - such as Dr. Jeff Masters and Greg Nordstrom - point out on their blogs, we are in an phase known as the Madden-Julian Oscillation. It "is a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days" (source, details: http://www.cpc.noaa.gov/products/precip/CWlink/MJO/MJO_1page_factsheet.pdf). We are in a phase now where enhanced convection can take place, and, in turn, higher potential for tropical development. Something to keep in mind.

In a nutshell:

- It has the potential in the next 48 hours to become Tropical Storm Bonnie and move west-northwest in this timeframe. As for Hurricane Bonnie, I think it's too early to say at this point.

- Its exact track is uncertain. It looks like south Florida could at least see some impacts from this disturbance - some wind and heavy rain. If it moves into the Gulf of Mexico, it could spell trouble for oil spill recovery efforts and have room to intensify. This invest needs to be closely monitored for the next few days, as there will be some impacts this weekend.

- Gainesville could only see a greater influx of moisture as the wave approaches and have higher rain chances. However, it depends on what path this wave takes.

- Wednesday's scheduled USAF reconnaissance mission should give us a better clue of what's happening, as well as better data to ingest into forecast models.

I will do my best to keep these updates going. I'm trying to get back into the weather blogging thing and work on my forecasting skills. Also, keep an eye on my Twitter feed (twitter.com/daweathaman) for the latest.

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