Dr. Jeff Masters' WunderBlog |
|
| Posted by: Dr. Jeff Masters, 17:07 GMT le 13 juin 2008 | +1 |
| Permalink | A A A |
|
Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
|
Tropical Blogs
Tropical Weather Stickers®
 |
46 ° F
Pluie fine
|
 |
 |
 |
 |
 |
Demandez votre Weather Sticker® gratuit |
 |
Téléchargez vos photos |
 |
Weather API for Developers NEW! |
 |
Devenez un membre du site |
 |
Trouvez-nous sur Facebook |
 |
Suivez-nous sur Twitter |
| Copyright © 2013 Weather Underground, Inc. | À propos de nous - Contact - Soutien - Emploi - Communiqués de presse - Conditions de service - Privacy Statement |
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 — Blog Index
Should this not be on YOUR on personal blog. Instead of a post....wow
Blob Watching
--------------------------------------
At 14:30 PM IST, Morning's Depression over north Bay of Bengal off Bangladesh coast moved in a westerly direction and lays centered at 21.5N 89.5E close to Bangladesh coast and about 170 kms southeast of Calcutta, India. The system is likely to move in a northwesterly direction and cross Bangladesh coast between 89.0 and 89.5E by today evening.
Tropical Cyclone Bulletin for Coastal India
===========================================
Under its influence, rainfall at most places with heavy to very heavy rainfall at a few places and extremely heavy falls (>25cm) at isolated places is likely over gangetic West Bengal and north Orrisa during next 48 hours. Fairly widespread rainfall with isolated heavy to very heavy falls is also likely over south Orrisa and Jarkhand during the same period.
Squally winds speed reaching 45-55 km/h are likely along and off north Orrisa and West Bengal coasts during next 24 hours. Sea condition is rough to very rough along and off these coasts. The Fishermen are advised not to venture into sea.
"...meteorology is an attempt to approximate chaos..."
it's as much art as science.....
Very well said!
The best we can do is use climatology as something as the norm. We have to look at the situation operationally and objectively (as it is happening now) to gauge whether these conditions are the norm.
Guestimation.
That's why we call it weather. You never know whether it will turn out the way you expect.
Busy today, but will check back in when I can....
SWAG: scientific wild @ssed guess
Good Chance of Strong to Severe Storms today 60%-70% chance
We in Human Psychology still have you beat.
Re: 179. Skyepony 3:29 AM GMT on June 14, 2008
Re: 189. atmoaggie 4:48 AM GMT on June 14, 2008
Although the terrible flooding in the Midwest is continuing, I wanted to respond to some open questions on this blog regarding how flood recurrence intervals are computed, how often they are updated depending on changing conditions, and how the corresponding FEMA floodplains are determined.
The FEMA Guidelines and Specifications for Flood Hazard Mapping Partners page contains links to most of the documents describing the procedures and technical specifications and requirements for determining recurrence intervals and floodplains. Quoting from Volume 1: Flood Studies and Mapping,
"An increase in the length of a stream gage record may also affect the flood discharge estimate. If the effective discharge was estimated by conducting a frequency analysis of a relatively short record of stream gage data, the base flood discharge estimate may be changed if newly available data are added. If stream gage data with a relatively long record(50 years or more) were used in the effective analyses, however, a few additional years usually will not cause significant changes in the base flood discharge estimate, unless a large-magnitude event occurred since the analyses were conducted. All frequency analyses are to be performed in accordance with the methods specified in Bulletin 17B, Guidelines for Determining Flood Flow Frequency (Interagency Advisory Committee on Water Data, 1982). The effective flood discharge shall be revised only if that discharge is outside the 90-percent confidence interval (higher than 95-percent confidence limit or lower than 5-percent confidence limits) of the newly computed flood discharge. [February 2002]"
The Bulletin 17B mentioned above is available from the USGS Guidelines for Determining Flood Flow Frequency page.
From reading the documents my understanding is that in general updates may be required by the FEMA Director, but the decisions to update are usually left to the FEMA regional offices. Updates are completed for different subregions every year. A search of updates may be performed by going to the Federal Register EPA Impact Statements site. A search using the words "change" and "elevation" seems to bring up all of the updates.
Although the updates are normally local and ongoing, FEMA is currently engaged in a national update effort called the "Flood Map Modernization Program". Here is FEMA's Map Modernization page with links to all of the documents. The program will involve digitization of many paper products, improved on-line access of data, and widespread updates of current FEMA maps. Quoting from the FAQ,
Q: What is Flood Map Modernization?
A: Flood Map Modernization (Map Mod) is FEMA's approach to updating the Nation's flood hazard maps. Map Mod transforms flood maps into reliable, easy-to-use, and readily available digital products. As a result, communities across the country can more easily obtain flood risk information to help make sound construction and mitigation decisions.
Q: Why do flood maps need to be updated?
A: Reliable information about flood risks is the first step in preventing and reducing losses. Today, more than two-thirds of the Nation's flood maps are more than ten years old, and therefore may not represent the true flood risks. Up-to-date flood hazard data and maps support an actuarially sound flood insurance system, enable wise floodplain management, and increase the Nation's flood hazard awareness.
[...]
A good short tutorial on calculating flood recurrence intervals is available courtesy of Dr. Eric M. Baer, Geology Program, Highline Community College via Carleton College: Teaching recurrence intervals.
A very good description of how FEMA's standards for hydrological and hydraulic modeling are translated locally into operational mode is given in Knox County Tennessee Stormwater Management Manual Section 8.4 Floodplain Management Regulations. For example,
"8.4.3.1 Hydrologic Modeling - Determining Peak Discharges
Peak discharges shall be determined for the 2-year, 10-year, 25-year, 100-year and 500-year
storm events. The peak discharges shall be determined for pre-development and post-development land use conditions, and shall be utilized as input to the hydraulic model that is used to determine floodplain elevations and other floodplain data.
Four methods are considered acceptable for determining peak discharges for the purpose of
floodplain data development, as follows:
1. gage analysis using statistical hydrologic methods;
2. Clark Unit Hydrograph;
3. the use of Tennessee Valley Authority (TVA) regression equations; and,
4. the use of a hydrologic model, such as USACE's HEC-1 or HEC-HMS.
The Director shall select the method that will be used on a case-by-case basis. The selection is based on the availability of existing hydrologic models and/or gage data in the same area as the proposed development, a history of flooding in the same area as, or downstream of, the proposed development, FEMA standards and requirements, and engineering judgment."[...](more)
The U.S. Army Corps of Engineers hydrological and hydraulic modeling software is available on the Hydrologic Engineering Center page.
Interesting to note that FEMA specifies USGS regional regression equations that are used in the National Flood Frequency program (see Program Documentation for V3), but Knox County has substituted TVA equations... apparently an exception in areas where the TVA exists. The differences between the USGS and TVA equations are outlined in the Knox County Tennessee Stormwater Management Manual, Volume 2 (Technical Guidance) Chapter 3.1 Introduction to Hydrologic Methods.
Finally, for a short and fairly non-technical research paper showing how a group in Croatia integrated the USACE hydrological and hydraulic models together with a meteorological model to determine flood recurrence intervals, see "HYDROLOGIC AND HYDRAULIC ANALYSIS OF LESS STUDIED WATERSHEDS" (pdf).
CIMSS 200mb vort Atl
Why not just post a link?
A link to what?
If people are not interested in my posts please put me on ignore, that will solve the problem.
I tend to put up long posts.
Viewing: 951 - 980
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 — Blog Index