North America To Act Like Magnet For Tropics Mid Sept As Pattern & MJO Becomes More Favourable

Written by on September 3, 2013 in Tropical, United States of America with 0 Comments

The tropics overall remain quiet and there I no immediate threat from any system out there at this time. We currently have a system bringing heavy downpours, gusty winds to the Yucatan and this feature will drift west into the Bay of Campeche tomorrow. The NHC gives this a low chance of development (20%) and will likely push into eastern Mexico, enhancing rainfall in coming days.

We have a slightly and I highlight the word ‘slightly’, more interesting 2 pronged feature now approaching the Leeward Islands. It’s a weak low followed by a wave but their in part, the same entity. This area has a better chance of development but over the next 5 days, the greatest threat from this elongated cluster of disturbed weather will be heavy rainfall and local gusty winds and squalls. The trouble is there’s an upper low fairly close to the north while a lot of dry air is around also and both these factors will keep development at a minimum.

The below satellite imagery shows the disturbance over the western Yucatan and the elongated low and wave approaching the Lesser Antilles. Notice the large area of convection through the Caribbean. Shear will keep this region UNFAVORABLE for development.

rb-l

Note the amount of dry air present over the western Atlantic at the moment in the below water vapour image. That like I say is a lot of the reason for lack of development potential, however this area shouldn’t be ignored as modelling takes this large canopy of disturbed weather WNW towards the Bahamas this weekend. There is always a chance that winds slacken towards the weekend and we get this large area to start bundling.

wv-l

[s2If current_user_can(access_s2member_level1)]

As for the MJO, the GFS ensemble is trying to push towards a more conducive phase 1 into 2 as you can see below.

ensplume_small

The INCREASED area of convection reflective of the MJO is seen over the Atlantic in the next 15 days

gfs

Plenty more waves look to come off Africa with a much more healthy wave train. It’s when you see this combined with a more conducive MJO and the North America pattern transitioning with building heights further north then the strongest positive anomalies sliding east, one must watch the activity floating west across the Atlantic.

rb-l

I know I show you the weekly CFSv2 500mb heights a lot but I think it’s got a pretty good handle on the upper pattern over the next few weeks and I want to highlight the setup which will have the North America acting somewhat like a magnet for the tropics especially the period between the 16-22. That could be the time to really watch for US threats.

The setup kicks in week 1 and 2 as heights build into the NW again but by week 3 the strongest positives are over eastern Canada which means the height field lowers on a large scale over the Gulf, Caribbean and western Atlantic with the atmosphere wanting to pull anything down there, TOWARDS the US coast.

wk1_wk2_20130901_z500

Week 3-4

wk3_wk4_20130901_z500

It’s a relatively benign pattern over the Lower 48 and looks like the tropics SHOULD should take centre stage. While even next week could get more interesting with the system approaching the Lesser Antilles, I recon it’s the stuff NOW crossing Africa which may be more noteworthy in the 10-15 day period as the big high develops over northeast North America.

wk3_wk4_20130901_NAsfcT

[/s2If][s2If is_user_logged_in() AND current_user_cannot(access_s2member_level1)]

That’s it, [s2Get constant=”S2MEMBER_CURRENT_USER_DISPLAY_NAME” /]!

To continue reading, you need to have a valid subscription to access premium content exclusive to members. Please join a subscription plan if you would like to continue.[/s2If][s2If !is_user_logged_in()]

Sign in to read the full forecast…

Not yet a member? Join today for unlimited access

Sign up to markvoganweather.com today to get unlimited access to Mark Vogan’s premium articles, video forecasts and expert analysis.
[/s2If]

Tags: , ,

Follow us

Connect with Mark Vogan on social media to get notified about new posts and for the latest weather updates.

Subscribe via RSS Feed Connect on YouTube

Leave a Reply

Top