Debby is having a hard time maintaining deep convection in the face of 25kt shear. The SST is 28C, but that warm water is quite shallow there too. It's located at 23.9N 43.3W and tracking NW at 15kts now, with a satellite-estimated intensity of 35kts and 1003mb... barely holding onto tropical storm status. The forecast is unchanged: fluctuate a bit in intensity and recurve by 55W.
At 21Z yesterday, the strong tropical wave near the Lesser Antilles was upgraded to TD5 based on an aircraft flight into it. Today at 21Z, it was further upgraded to TS Ernesto, again based on aircraft recon. The storm is experiencing decent westerly vertical wind shear, so the low-level center is displaced to the west from the deep convection. Recall that this wave was born in the Ethiopian Highlands way back on August 10 or so, and exited Africa on August 17.
At 19Z today, Ernesto was located at 14.1N 67.3W. The intensity is 40kts and 1004mb... this may be adjusted slightly for the official 21Z advisory.
The forecast for Ernesto is very interesting, particularly for the Gulf coast. Over the next couple of days, it is expected to maintain its WNW heading and somewhat formidable shear, but after that, it enters lower shear, and VERY high oceanic heat content in the western Caribbean. In 5 days, it should pass between Yucatan and Cuba, heading in to the Gulf of Mexico as a possibly powerful hurricane. There is too much uncertainly beyond 5 days, but once in the Gulf, it HAS to hit somewhere.
Elsewhere, a new potent tropical wave is introduced off the African coast around 18W with an embedded 1008mb Low. We're now entering the heart of the "Cape Verde season", so these all need to be watched closely.
Also, today is the 1-year anniversary of Hurricane Katrina's Florida landfall.
http://einstein.atmos.colostate.edu/~mcnoldy/tropics/katrina/Katrina_25Aug05.gif
Please visit my tropical Atlantic headquarters.
25 August 2006
24 August 2006
Debby struggling...
Debby is presently experiencing the coldest SSTs of its journey thus far, around 26C. There is only minimal convection associated with the storm now, and it looks rather ragged. Over the next few days, the SSTs will increase again (up to almost 29C), likely allowing the storm to reintensify, and PERHAPS finally reach hurricane status.
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skip this part if you're just interested in the headlines...
The SST is an important ingredient in intensity forecasting, but far from the only one. From a strictly thermodynamic viewpoint (disregarding shear, eyewall replacements, land, dry air entrainment, boundary layer humidity, other moisture-related issues), the outflow temperature is just as important. If you assume the outflow of the hurricane to be at about 200mb, you can use the temperature there and find the difference between that and the temperature at the inflow layer (sea surface). It's this difference that controls the lapse rate and instability in the hurricane near-environment. Using Debby as an example (and taking the diagnosed SST along the forecast track from a statistical model called SHIPS), we get the following:
-- Thursday morning SST: 26.1C
-- Thursday morning outflow temp: -53.0C
-- Thursday morning's DIFFERENCE: 79.1C
-- Saturday morning SST: 28.5C
-- Saturday morning outflow temp: -54.1C
-- Saturday morning's DIFFERENCE: 82.6C
So, in a couple days, the temperature difference between the inflow and outflow of the storm will be 3.5C greater, which in the tropics is a big deal, because lapse rates typically vary VERY little there. Taking this morning's data and tweaking it a little just to make a point, suppose the outflow temperature were -56.5C... you'd get exactly the same healthy lapse rate as what is forecast for Saturday morning! In the tropics however, SSTs are of more interest because the outflow temperature typically changes so little. There are subtleties involved with this explanation, but that's the basics!
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The latest intensity estimate (15Z) for Debby is 45kts and 1000mb, and heading WNW at 17kts. It is located at 20.4N 37.8W, basically in the middle of the basin, and heading for even more open ocean. It is forecast to slowly strengthen as it turns to the NW then N, recurving by 55W.
The strong tropical wave that was near 11N 55W yesterday is near 12N 61W today, and not organized enough to be upgraded to a tropical depression, but it is still convectively active and showing signs of at least a mid-level circulation, if not low-level as well. It's tracking W at 15kts and has a 1009mb Low embedded within it. This could be upgraded to TD5 or TS Ernesto within the next 24 hours, and in the long run, stands a very good chance at reaching hurricane intensity as it cruises through the central and western Caribbean -- low shear, 30C SSTs, and significant oceanic heat content!
Please visit my tropical Atlantic headquarters.
[**********
skip this part if you're just interested in the headlines...
The SST is an important ingredient in intensity forecasting, but far from the only one. From a strictly thermodynamic viewpoint (disregarding shear, eyewall replacements, land, dry air entrainment, boundary layer humidity, other moisture-related issues), the outflow temperature is just as important. If you assume the outflow of the hurricane to be at about 200mb, you can use the temperature there and find the difference between that and the temperature at the inflow layer (sea surface). It's this difference that controls the lapse rate and instability in the hurricane near-environment. Using Debby as an example (and taking the diagnosed SST along the forecast track from a statistical model called SHIPS), we get the following:
-- Thursday morning SST: 26.1C
-- Thursday morning outflow temp: -53.0C
-- Thursday morning's DIFFERENCE: 79.1C
-- Saturday morning SST: 28.5C
-- Saturday morning outflow temp: -54.1C
-- Saturday morning's DIFFERENCE: 82.6C
So, in a couple days, the temperature difference between the inflow and outflow of the storm will be 3.5C greater, which in the tropics is a big deal, because lapse rates typically vary VERY little there. Taking this morning's data and tweaking it a little just to make a point, suppose the outflow temperature were -56.5C... you'd get exactly the same healthy lapse rate as what is forecast for Saturday morning! In the tropics however, SSTs are of more interest because the outflow temperature typically changes so little. There are subtleties involved with this explanation, but that's the basics!
**********]
The latest intensity estimate (15Z) for Debby is 45kts and 1000mb, and heading WNW at 17kts. It is located at 20.4N 37.8W, basically in the middle of the basin, and heading for even more open ocean. It is forecast to slowly strengthen as it turns to the NW then N, recurving by 55W.
The strong tropical wave that was near 11N 55W yesterday is near 12N 61W today, and not organized enough to be upgraded to a tropical depression, but it is still convectively active and showing signs of at least a mid-level circulation, if not low-level as well. It's tracking W at 15kts and has a 1009mb Low embedded within it. This could be upgraded to TD5 or TS Ernesto within the next 24 hours, and in the long run, stands a very good chance at reaching hurricane intensity as it cruises through the central and western Caribbean -- low shear, 30C SSTs, and significant oceanic heat content!
Please visit my tropical Atlantic headquarters.
23 August 2006
TD4 upgraded to TS Debby...
At 03Z today (Tuesday night in the US), TD4 was upgraded to the forth named storm of the season, Debby. This was based on infrared and microwave satellite imagery. As of 15Z, the intensity estimate is 45kts and 1000mb. It's located about 5 degrees due west of the Cape Verde islands.
The forecast for Debby is gradual strengthening, possibly reaching minimal hurricane intensity during the weekend. The track should follow a WNW to NW course, which will momentarily take the storm over cool water (25C), but in about 3 days, will be back over 28-29C water. However, combating that increase in SST is an anticipated increase in southwesterly vertical wind shear.
Elsewhere, the tropical wave that was near 50W yesterday is still lacking an organized low-level circulation, but the mid-level circulation is located at about 11N 55W and tracking W at 15kts. It has been convectively active in bursts, and chances of formation seem fairly high by the end of the week. This is the wave that exited Africa back on August 17. If this develops, the forecast would be for a WNW track through the heart of the Caribbean, likely becoming at least a tropical storm, if not a hurricane. The next number/name on deck is 5/Ernesto.
Please visit my tropical Atlantic headquarters.
The forecast for Debby is gradual strengthening, possibly reaching minimal hurricane intensity during the weekend. The track should follow a WNW to NW course, which will momentarily take the storm over cool water (25C), but in about 3 days, will be back over 28-29C water. However, combating that increase in SST is an anticipated increase in southwesterly vertical wind shear.
Elsewhere, the tropical wave that was near 50W yesterday is still lacking an organized low-level circulation, but the mid-level circulation is located at about 11N 55W and tracking W at 15kts. It has been convectively active in bursts, and chances of formation seem fairly high by the end of the week. This is the wave that exited Africa back on August 17. If this develops, the forecast would be for a WNW track through the heart of the Caribbean, likely becoming at least a tropical storm, if not a hurricane. The next number/name on deck is 5/Ernesto.
Please visit my tropical Atlantic headquarters.
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