Invest 99L May Slowly Develop
The tropics have come to life in the last couple days. Very briefly I should mention that a very large, strengthening typhoon, Saola, is bearing down on the island nation on Taiwan and has the potential to casue life threatening floods and mudslides. The JTWC says the system has maximum sustained winds of 55kts. I do not claim to know better than the experts, but this is absolutely ridiculous as Figure 1 shows Saola is almost certainly a typhoon.
Figure 1: Tropical Storm Saola.
Also in the West Pacifc, Tropical Storm Damrey is heading for a brush with southern Japan and an eventual landfall in northern China, with flooding being the main threat from this weak system currently only packing winds of 40mph.
99L May Develop
For the first time in a while, we are tracking an area of interest in the Atlantic with a real chance to develop. This area, Invest 99L, is located approximately 900 miles SW of the Cape Verde Islands, and is moving steadily westward at 10-15mph. 99L has changed little in organization today, with recent satellite images showing perhaps a slight improvement. This should be the general trend for the next 2 days or so. 99L is located in a low wind shear environment and in a fairly moist environment, with most of the Saharan Air Layer to the north of the system. However, this position, while keeping 99L out of the SAL, is also providing it with its biggest problem: Like most systems within 10 degrees of the equator (99L is at 9 degrees N), the system will struggle to get the spin necessary to develop. Despite this, however, many models do indicate gradual development. The National Hurricane Center gives 99L a 20% chance of developing in the next 48 hours. I agree with this percentage, but think that there is a higher chance than that, maybe 50-60%, of it developing at any point in its lifespan. Should development occur, track and intensity are very uncertain right now. Long term intensity will likely depend on track. At least in the short term, there is high confidence in a continued W to WNW motion, bringing the system near the Lesser Antilles. It should be gradually organizing during this time, and could arrive in the Antilles as something between a tropical depression and moderate tropical storm. Beyond that, however, track is highly uncertain. Here's the model breakdown:
GFS: Continued western track into Caribbean, slowly strengthens but then dissipates once it gets into the Caribbean. It should be noted that the 12z GFS backed off on its intensity forecast, which hurts my confidence on this system developing at all. We will have to see if this trend continues.
GFS ensembles: Several of them take the system north of the Caribbean and strengthen it significantly, making it a hurricane with landfall on the East Coast or a track out to sea.
ECMWF: Has shown no or very little development consistently, not uncommon for this model before development. If it catches on then confidence on something forming will go way up.
CMC: Has been taking a northerly track and strengthening the storm more, indicating possible East Coast impacts.
UKMET: Has not shown much development but has shown anything that does develop heading west into the Caribbean.
The key will be how fast the system develops. A stronger system is more likely to take the northerly track, while a weaker system would take the southerly track. It's too hard to speculate very much on this right now since we don't have a developed system yet. The same goes for intensity. The SHIPS model makes 99L a hurricane, but it almost always forecasts strengthening of any invest that forms, so I wouldn't put much faith in this. The bottom line is that everybody should be watching this, whether they are in the Caribbean or anywhere on the US coastline as very little is certain about this system right now.
Figure 2: Invest 99L
I will be working at the Blue Hill Observatory from 7:30-2:30 for the next three days so I will only be on later in the afternoon for these days. Don't miss me too much.
Thanks for reading!