Two Atlantic Invests; Prapiroon Organizes

By: MAweatherboy1 , 11:41 PM GMT on October 08, 2012

We are watching two invests in the Atlantic basin this evening. The first is invest 97L. 97L is a sprawling system, with convection starting in the east central Bahamas and extending a couple hundred miles east. As of now, none of the reliable computer models develop this disturbance, and with upper level winds becoming even less favorable, development is highly unlikely. The National Hurricane Center is currently giving 97L a 10% chance of development in the next 48 hours, and I agree with this. While development is unlikely, enhanced shower and thunderstorm activity is likely for the Bahamas and surrounding areas for the next day or two.

Figure 1: Invest 97L, showing a large but very disorganized cluster of showers and thunderstorms. These should steadily weaken and become more disorganized in the next couple days.

98L May Develop Eventually
The other invest being tracked right now is 98L, which was designated this morning. 98L is currently located about 1500 miles ESE of the Lesser Antilles and is moving WNW at 15-20mph. 98L is definitely the more interesting of the two invests as several models are indicating some development of the system. One of the more aggressive models has been the GFS. As of right now, the National Hurricane Center gives 98L a 10% chance of development in the next 48 hours. I do not foresee any chance development in the next 48 hours, but beyond that things could get interesting. Right now 98L is mostly embedded in the ITCZ, and it is also at a very low latitude. Being stuck in the ITCZ prevents 98L from really gaining its own identity as a system and developing. The low latitude prevents the system from gaining spin and developing. I believe both of these issues will eventually be solved, and it will depend on upper level conditions to determine whether the system develops. It is currently too far out to know specifics, but here are two possible scenarios if development occurs.
1. 98L organizes faster than expected, skirts the northern Caribbean islands, then sharply turns out to sea as it intensifies. The GFS has been showing this solution.
2. 98L is slow to organize but does not dissipate and gets into the Caribbean further south. Beyond here several things could happen, ranging from dissipation due to unfavorable upper level conditions to significant intensification over warm waters with a helpful MJO pulse.
As of right now, I would say there is a 40% chance of no development, a 35% chance of scenario 1, and a 25% chance of scenario 2.

Figure 2: The East Atlantic, with 98L at the bottom left of the image.

West Pacific Remains Active
In the West Pacific, the main feature right now is Tropical Storm Prapiroon. Prapiroon currently has maximum 1 minute sustained winds of 60kts, or about 70mph, according to the Joint Typhoon Warning Center. Prapiroon has been organizing steadily today, but not rapidly. The official JTWC forecast indicates steady strengthening for the next 3 days, with a peak intensity of 100kts, followed by slight weakening on days 4 and 5. I find this intensity forecast to be quite difficult. On the one hand, basically every West Pacific storm over favorable conditions like Prapiroon is has rapidly intensified. On the other hand, microwave imagery is not suggesting any organized eyewall forming, which would indicate only slow strengthening is likely. My thinking is that strengthening will be slow for the next 12-24 hours, followed by a burst of rapid intensification as an eyewall does form. My estimated peak intensity is 110kts, a bit higher than the official forecast. The track forecast is also a challenge. The JTWC is currently hinting at a continued W/WNW motion for the next 2-3 days, followed by a sharp northeast turn out to sea as the ridge steering it breaks down. I think the scenario JTWC is showing is way to far out to sea. I anticipate a slower turn, bringing the system closer to Japan. I don't expect direct impacts, but high surf and rip currents will be a concern. There's plenty of time to watch this one and a lot will change, so stay tuned.

Figure 3: Official JTWC forecast track of Prapiroon.

Figure 4: Latest microwave image of Prapiroon. I do not see any rapidly developing eyewall that would suggest RI is imminent.

Also in the West Pacific, the remnants of Gaemi have essentially dissipated. A few days ago I mentioned there was a slight chance at regeneration in the Bay of Bengal as some GFS runs had suggested, but this will not be the case.

* All other basins, including the East Pacific, are quiet, with no development expected in the next 5 days.
* A severe weather event is possible for the central US towards the end of the week. The Storm Prediction Center has not highlighted any risk areas for this period yet, but that should not come as a surprise as confidence is low this far out. I'll provide more details if necessary in a couple days.
* The chunk of cold weather that brought numerous record low temperatures to the central US over the past couple days is pushing eastward, losing some of its punch as it goes. It will not be long before it pushed out of the country, and as Figure 5 shows warm air is likely to take its place.

Figure 5: Climate Prediction Center 6-10 day temperature outlook, showing the current cold blast leaving and warmer than average temperatures returning for most.
* There was some interesting solar weather last night and this morning. A CME produced by a solar flare a few days ago hit Earth last night and produced a moderate geomagnetic storm. The worst is over but residual minor storming is still possible. We also saw an M2.3 class solar flare produced by a sunspot off the NE limb of the Sun, not yet visible to us. It has fallen quiet since, possible a temporary lull or possibly a sign the spot is beginning to decay. We'll get a much better idea when the spot rotates into view in the next couple days. Another sunspot is hiding off the SE limb and appears to be growing more active as it just produced a C class flare. Again, we'll know more about it when we can actually see it.

Figure 6: The sunspot off the NE limb lights up after producing an M class solar flare.

Thank you for reading, and have a great week!

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

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9. WunderAlertBot (Admin)
9:05 PM GMT on October 11, 2012
MAweatherboy1 has created a new entry.
8. HadesGodWyvern (Mod)
1:18 PM GMT on October 11, 2012
RSMC Reunion has been monitoring 91S awhile for development.

The season start is a little normal at this time. They usually start getting disturbances or depressions in October.
Member Since: December 31, 1969 Posts: Comments:
7. HadesGodWyvern (Mod)
1:15 PM GMT on October 11, 2012
Reunion Tropical Cyclone Outlook
15:00 PM RET October 11 2012

Convective activity is moderate to strong, but fluctuating, and concentrated between 65.0E and 85.0E
north of 12.0S. In this area, multispectral satellite imagery suggests a broad clockwise circulation whose the center can be localized very approximately near 6.7S 74.5E at 0900 AM UTC. The central pressure is estimated at 1007 hPa (observation Diego-Garcia at 0900 AM UTC). 0355 AM UTC ASCAT pass shows winds at about 10-15 knots, reaching 20-25 kt in the southern semi-circle.

The low is currently well supplied poleward. Equatorward low level inflow is weaker, but should
improve within the next days. Upper level vertical wind shear is moderate on the western edge of
high pressures located in the east. Within the next 72 hours, available numerical weather prediction models forecast that this low will keep a fast enough movement west southwestward, and should slowly deepen with fairly good environmental conditions. Saturday and especially Sunday, it is expected that vertical wind shear will decrease and so the low should more clearly deepen.

For the next 36 hours, development of a tropical depression is not expected. Beyond, potential becomes fair to good.
Member Since: December 31, 1969 Posts: Comments:
6. HadesGodWyvern (Mod)
6:24 AM GMT on October 11, 2012
India Meteorological Department
Tropical Cyclone Advisory #3
8:30 AM IST October 11 2012

SUBJECT: Depression Overland Bangladesh

At 3:00 AM UTC The depression over northeast Bay of Bengal moved northeastward and crossed Bangladesh coast near Hatia between 0030-0130 AM UTC of today. Depression BOB01-2012 now lays centered over Bangladesh and adjoining Tripura near 23.0N 91.5E, or 100 km south of Agartala.

The system is likely to move northeastwards and weaken gradually into a well marked low pressure area during next 24 hrs.
Member Since: December 31, 1969 Posts: Comments:
5. HadesGodWyvern (Mod)
10:33 PM GMT on October 10, 2012
of course this was much earlier today.. the next advisory will be after complete landfall most likely
Member Since: December 31, 1969 Posts: Comments:
4. HadesGodWyvern (Mod)
10:32 PM GMT on October 10, 2012
India Meteorological Department
Tropical Cyclone Advisory #1
20:30 PM IST October 10 2012

SUBJECT: Depression Over Northeast Bay Of Bengal

At 15:00 PM UTC, Latest satellite imagery indicates that a depression has formed over northeast Bay of Bengal and lays centered near 21.0N 91.0E or about 350 km southeast of Kolkata (India), 150 km southeast of Khepurara (Bangladesh), and 150 km south of Hatia (India). The system is likely to intensify further, move northward, and cross Bangladesh coast near Hatia tomorrow..

According to satellite imageries, the intensity of the System is T1.5. The lowest cloud top temperature is about -70C. Associated broken low/medium clouds with embedded intense to very intense convection seen over Bay of Bengal north of 18.5N east 90.5E

3 minutes sustained maximum surface wind speed is estimated to be about 25 knots gusting to 35 knots and central pressure is about 1003 hPa. The state of the sea is rough to very rough around the system center. The 24 hrs pressure tendency is negative and about 1 hpa along Bangladesh coast.

Considering the environmental features, the Madden Julian Oscillation index currently lies over phase 6 with Amplitude of 1. As per statistical and nwp model predictions, It is expected to lie in phase 7 during next 2-3 days with decrease in amplitude. Hence it is not favourable for further intensification. The sea surface temperature is about 29-30C over north bay of bengal. The ocean thermal energy is 50-60 kj/cm2 around the system center it decreases towards bangladesh coast. The upper tropospheric ridge lies along 20.0N and hence close to system center. A trough in mid-tropospheric westerlies roughly runs along 80.0E to the north of 18.0N. It is likely to steer the system northeastwards. The low level convergence has increased during past 12 hrs as well as upper level divergence and lower level relative vorticity. The vertical wind shear between 200 and 850 hpa levels is low to moderate (10-20 knots) around system center. However, it increases towards bangladesh coast. Considering the nwp model guidance, most of the models do not suggest further intensification of the system.
Member Since: December 31, 1969 Posts: Comments:
3. MAweatherboy1
1:28 AM GMT on October 09, 2012
Quoting pcola57:
Good job wx97, quite an accomplishment..
Keep up the good work.. :)

Thanks! Except I'm MA :)
Member Since: December 31, 1969 Posts: Comments:
2. pcola57
1:12 AM GMT on October 09, 2012
Good job wx97, quite an accomplishment..
Keep up the good work.. :)
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1. wxchaser97
11:48 PM GMT on October 08, 2012
Thanks MA, happy 50th blog.
Member Since: December 31, 1969 Posts: Comments:

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Average 20 year old weather nerd. Plymouth State University Meteorology, Class of 2018. NOAA Hollings scholar. Summer 2016 intern at NWS Boston.

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